diff --git a/.idea/misc.xml b/.idea/misc.xml
index aa89dc92..c27c7ebd 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -74,7 +74,7 @@
   <component name="ProjectModuleManager">
     <modules />
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_6" assert-keyword="true" jdk-15="true" project-jdk-name="1.7" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_6" assert-keyword="true" jdk-15="true" project-jdk-name="1.6" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/build/classes" />
   </component>
   <component name="PropertiesComponent">
diff --git a/android-app/src/main/java/org/solovyev/android/calculator/AndroidCalculatorDisplayView.java b/android-app/src/main/java/org/solovyev/android/calculator/AndroidCalculatorDisplayView.java
index 92b49172..6587587a 100644
--- a/android-app/src/main/java/org/solovyev/android/calculator/AndroidCalculatorDisplayView.java
+++ b/android-app/src/main/java/org/solovyev/android/calculator/AndroidCalculatorDisplayView.java
@@ -128,7 +128,7 @@ public class AndroidCalculatorDisplayView extends AutoResizeTextView implements
 
 						AndroidCalculatorDisplayView.this.state = state;
 						if (state.isValid()) {
-							setTextColor(getResources().getColor(R.color.cpp_default_text_color));
+							setTextColor(getResources().getColor(R.color.cpp_text));
 							setText(text);
 
 							adjustTextSize();
@@ -136,7 +136,7 @@ public class AndroidCalculatorDisplayView extends AutoResizeTextView implements
 						} else {
 							// update text in order to get rid of HTML tags
 							setText(getText().toString());
-							setTextColor(getResources().getColor(R.color.cpp_display_error_text_color));
+							setTextColor(getResources().getColor(R.color.cpp_text_error));
 
 							// error messages are never shown -> just greyed out text (error message will be shown on click)
 							//setText(state.getErrorMessage());
diff --git a/android-app/src/main/java/org/solovyev/android/calculator/view/AngleUnitsButton.java b/android-app/src/main/java/org/solovyev/android/calculator/view/AngleUnitsButton.java
index 80244601..c138de07 100644
--- a/android-app/src/main/java/org/solovyev/android/calculator/view/AngleUnitsButton.java
+++ b/android-app/src/main/java/org/solovyev/android/calculator/view/AngleUnitsButton.java
@@ -67,9 +67,9 @@ public class AngleUnitsButton extends DirectionDragButton {
 		final int color;
 		final Resources resources = getResources();
 		if (isCurrentAngleUnits(directionText)) {
-			color = resources.getColor(R.color.cpp_selected_angle_unit_text_color);
+			color = resources.getColor(R.color.cpp_selected_angle_unit_text);
 		} else {
-			color = resources.getColor(R.color.cpp_default_text_color);
+			color = resources.getColor(R.color.cpp_text);
 		}
 		return color;
 	}
diff --git a/android-app/src/main/java/org/solovyev/android/calculator/view/NumeralBasesButton.java b/android-app/src/main/java/org/solovyev/android/calculator/view/NumeralBasesButton.java
index 0ae944b2..d2640977 100644
--- a/android-app/src/main/java/org/solovyev/android/calculator/view/NumeralBasesButton.java
+++ b/android-app/src/main/java/org/solovyev/android/calculator/view/NumeralBasesButton.java
@@ -65,9 +65,9 @@ public class NumeralBasesButton extends DirectionDragButton {
 	int getDirectionTextColor(@Nonnull String directionText) {
 		final int color;
 		if (isCurrentNumberBase(directionText)) {
-			color = getResources().getColor(R.color.cpp_selected_angle_unit_text_color);
+			color = getResources().getColor(R.color.cpp_selected_angle_unit_text);
 		} else {
-			color = getResources().getColor(R.color.cpp_default_text_color);
+			color = getResources().getColor(R.color.cpp_text);
 		}
 		return color;
 	}
diff --git a/android-app/src/main/java/org/solovyev/android/calculator/widget/AbstractCalculatorWidgetProvider.java b/android-app/src/main/java/org/solovyev/android/calculator/widget/AbstractCalculatorWidgetProvider.java
index f80ea8b0..4e53e0fb 100644
--- a/android-app/src/main/java/org/solovyev/android/calculator/widget/AbstractCalculatorWidgetProvider.java
+++ b/android-app/src/main/java/org/solovyev/android/calculator/widget/AbstractCalculatorWidgetProvider.java
@@ -95,7 +95,7 @@ abstract class AbstractCalculatorWidgetProvider extends AppWidgetProvider {
 	@Nonnull
 	private String getCursorColor(@Nonnull Context context) {
 		if (cursorColor == null) {
-			cursorColor = Integer.toHexString(context.getResources().getColor(R.color.cpp_widget_cursor_color)).substring(2);
+			cursorColor = Integer.toHexString(context.getResources().getColor(R.color.cpp_widget_cursor)).substring(2);
 		}
 		return cursorColor;
 	}
@@ -198,9 +198,9 @@ abstract class AbstractCalculatorWidgetProvider extends AppWidgetProvider {
 	private void updateDisplayState(@Nonnull Context context, @Nonnull RemoteViews views, @Nonnull CalculatorDisplayViewState displayState) {
 		if (displayState.isValid()) {
 			views.setTextViewText(R.id.calculator_display, displayState.getText());
-			views.setTextColor(R.id.calculator_display, context.getResources().getColor(R.color.cpp_default_text_color));
+			views.setTextColor(R.id.calculator_display, context.getResources().getColor(R.color.cpp_text));
 		} else {
-			views.setTextColor(R.id.calculator_display, context.getResources().getColor(R.color.cpp_display_error_text_color));
+			views.setTextColor(R.id.calculator_display, context.getResources().getColor(R.color.cpp_text_error));
 		}
 	}
 
diff --git a/android-app/src/main/res/drawable/metro_button_dark_shape.xml b/android-app/src/main/res/drawable/metro_button_dark_shape.xml
index 2165b29a..c51c55ac 100644
--- a/android-app/src/main/res/drawable/metro_button_dark_shape.xml
+++ b/android-app/src/main/res/drawable/metro_button_dark_shape.xml
@@ -21,6 +21,6 @@
   -->
 
 <shape xmlns:android="http://schemas.android.com/apk/res/android">
-	<solid android:color="@color/cpp_metro_button_background"/>
+	<solid android:color="@color/cpp_metro_button"/>
 	<corners android:radius="1dp"/>
 </shape>
\ No newline at end of file
diff --git a/android-app/src/main/res/drawable/metro_button_green_shape.xml b/android-app/src/main/res/drawable/metro_button_green_shape.xml
index 2887709b..d9f9f488 100644
--- a/android-app/src/main/res/drawable/metro_button_green_shape.xml
+++ b/android-app/src/main/res/drawable/metro_button_green_shape.xml
@@ -21,6 +21,6 @@
   -->
 
 <shape xmlns:android="http://schemas.android.com/apk/res/android">
-	<solid android:color="@color/cpp_metro_green_color"/>
+	<solid android:color="@color/cpp_metro_green"/>
 	<corners android:radius="1dp"/>
 </shape>
\ No newline at end of file
diff --git a/android-app/src/main/res/drawable/metro_button_light_shape.xml b/android-app/src/main/res/drawable/metro_button_light_shape.xml
index 78e13a77..36d69510 100644
--- a/android-app/src/main/res/drawable/metro_button_light_shape.xml
+++ b/android-app/src/main/res/drawable/metro_button_light_shape.xml
@@ -21,6 +21,6 @@
   -->
 
 <shape xmlns:android="http://schemas.android.com/apk/res/android">
-	<solid android:color="@color/cpp_metro_light_button_background"/>
+	<solid android:color="@color/cpp_metro_button_light"/>
 	<corners android:radius="1dp"/>
 </shape>
diff --git a/android-app/src/main/res/drawable/metro_button_purple_shape.xml b/android-app/src/main/res/drawable/metro_button_purple_shape.xml
index a994ce3b..1ffbb8fd 100644
--- a/android-app/src/main/res/drawable/metro_button_purple_shape.xml
+++ b/android-app/src/main/res/drawable/metro_button_purple_shape.xml
@@ -21,6 +21,6 @@
   -->
 
 <shape xmlns:android="http://schemas.android.com/apk/res/android">
-	<solid android:color="@color/cpp_metro_purple_color"/>
+	<solid android:color="@color/cpp_metro_purple"/>
 	<corners android:radius="1dp"/>
 </shape>
\ No newline at end of file
diff --git a/android-app/src/main/res/drawable/metro_green_list_item.xml b/android-app/src/main/res/drawable/metro_green_list_item.xml
index 0ba94d5a..06ddd49f 100644
--- a/android-app/src/main/res/drawable/metro_green_list_item.xml
+++ b/android-app/src/main/res/drawable/metro_green_list_item.xml
@@ -28,25 +28,25 @@
 	<item a:state_focused="false" a:state_selected="false" a:state_pressed="false"
 		  a:drawable="@android:color/transparent"/>
 	<item a:state_focused="false" a:state_selected="true" a:state_pressed="false"
-		  a:drawable="@color/cpp_metro_green_color"/>
+		  a:drawable="@color/cpp_metro_green"/>
 
 	<!-- Focused states -->
 	<item a:state_focused="true" a:state_selected="false" a:state_pressed="false"
-		  a:drawable="@color/cpp_metro_green_color"/>
+		  a:drawable="@color/cpp_metro_green"/>
 	<item a:state_focused="true" a:state_selected="true" a:state_pressed="false"
-		  a:drawable="@color/cpp_metro_green_color"/>
+		  a:drawable="@color/cpp_metro_green"/>
 
 	<!-- Pressed -->
 	<!--    Non focused states -->
 	<item a:state_focused="false" a:state_selected="false" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_green_color"/>
+		  a:drawable="@color/cpp_metro_green"/>
 	<item a:state_focused="false" a:state_selected="true" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_green_color"/>
+		  a:drawable="@color/cpp_metro_green"/>
 
 	<!--    Focused states -->
 	<item a:state_focused="true" a:state_selected="false" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_green_color"/>
+		  a:drawable="@color/cpp_metro_green"/>
 	<item a:state_focused="true" a:state_selected="true" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_green_color"/>
+		  a:drawable="@color/cpp_metro_green"/>
 
 </selector>
diff --git a/android-app/src/main/res/drawable/metro_purple_list_item.xml b/android-app/src/main/res/drawable/metro_purple_list_item.xml
index 0c54af47..973b7a24 100644
--- a/android-app/src/main/res/drawable/metro_purple_list_item.xml
+++ b/android-app/src/main/res/drawable/metro_purple_list_item.xml
@@ -28,24 +28,24 @@
 	<item a:state_focused="false" a:state_selected="false" a:state_pressed="false"
 		  a:drawable="@android:color/transparent"/>
 	<item a:state_focused="false" a:state_selected="true" a:state_pressed="false"
-		  a:drawable="@color/cpp_metro_purple_color"/>
+		  a:drawable="@color/cpp_metro_purple"/>
 
 	<!-- Focused states -->
 	<item a:state_focused="true" a:state_selected="false" a:state_pressed="false"
-		  a:drawable="@color/cpp_metro_purple_color"/>
+		  a:drawable="@color/cpp_metro_purple"/>
 	<item a:state_focused="true" a:state_selected="true" a:state_pressed="false"
-		  a:drawable="@color/cpp_metro_purple_color"/>
+		  a:drawable="@color/cpp_metro_purple"/>
 
 	<!-- Pressed -->
 	<!--    Non focused states -->
 	<item a:state_focused="false" a:state_selected="false" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_purple_color"/>
+		  a:drawable="@color/cpp_metro_purple"/>
 	<item a:state_focused="false" a:state_selected="true" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_purple_color"/>
+		  a:drawable="@color/cpp_metro_purple"/>
 
 	<!--    Focused states -->
 	<item a:state_focused="true" a:state_selected="false" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_purple_color"/>
+		  a:drawable="@color/cpp_metro_purple"/>
 	<item a:state_focused="true" a:state_selected="true" a:state_pressed="true"
-		  a:drawable="@color/cpp_metro_purple_color"/>
+		  a:drawable="@color/cpp_metro_purple"/>
 </selector>
diff --git a/android-app/src/main/res/layout/history_fragment.xml b/android-app/src/main/res/layout/history_fragment.xml
index e2f83f45..c81825d1 100644
--- a/android-app/src/main/res/layout/history_fragment.xml
+++ b/android-app/src/main/res/layout/history_fragment.xml
@@ -50,8 +50,8 @@
 			a:layout_gravity="bottom|right"
 			a:layout_margin="16dp"
 			a:src="@drawable/ic_delete_white_36dp"
-			fab:fab_colorNormal="@color/cpp_metro_button_background"
-			fab:fab_colorPressed="@color/cpp_metro_button_background"
+			fab:fab_colorNormal="@color/cpp_metro_button"
+			fab:fab_colorPressed="@color/cpp_metro_button"
 			fab:fab_colorRipple="?attr/colorControlHighlight" />
 	</FrameLayout>
 </LinearLayout>
\ No newline at end of file
diff --git a/android-app/src/main/res/values-v21/theme.xml b/android-app/src/main/res/values-v21/theme.xml
new file mode 100644
index 00000000..dc7c52e0
--- /dev/null
+++ b/android-app/src/main/res/values-v21/theme.xml
@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  ~ Copyright 2013 serso aka se.solovyev
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~    http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  ~
+  ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  ~ Contact details
+  ~
+  ~ Email: se.solovyev@gmail.com
+  ~ Site:  http://se.solovyev.org
+  -->
+
+<resources>
+
+	<style name="Theme" parent="Theme.Base">
+		<item name="android:colorPrimary">@color/cpp_metro_button</item>
+		<item name="android:colorPrimaryDark">@color/cpp_metro_button_dark</item>
+	</style>
+
+	<style name="Theme.Dialog" parent="Theme.Base.Dialog">
+		<item name="android:colorPrimary">@color/cpp_metro_button</item>
+		<item name="android:colorPrimaryDark">@color/cpp_metro_button_dark</item>
+	</style>
+
+</resources>
\ No newline at end of file
diff --git a/android-app/src/main/res/values/colors.xml b/android-app/src/main/res/values/colors.xml
index 04b048dc..48dc0cf6 100644
--- a/android-app/src/main/res/values/colors.xml
+++ b/android-app/src/main/res/values/colors.xml
@@ -1,5 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--
+<?xml version="1.0" encoding="utf-8"?><!--
   ~ Copyright 2013 serso aka se.solovyev
   ~
   ~ Licensed under the Apache License, Version 2.0 (the "License");
@@ -23,22 +22,23 @@
 
 <resources>
 	<color name="cpp_list_divider">#ff2e2e2e</color>
-	<color name="cpp_default_text_color">#ffffffff</color>
-	<color name="cpp_display_error_text_color">#ff393939</color>
-	<color name="cpp_button_text_color">#ffffffff</color>
-	<color name="cpp_button_operator_text_color">#ffffff99</color>
-	<color name="cpp_button_ce_text_color">#ffffffff</color>
-	<color name="cpp_selected_angle_unit_text_color">#ffffff99</color>
+	<color name="cpp_text">#ffeeeeee</color>
+	<color name="cpp_text_error">#ff393939</color>
+	<color name="cpp_button_text">#ffffffff</color>
+	<color name="cpp_button_text_operator">#ffffff99</color>
+	<color name="cpp_button_text_ce">#ffffffff</color>
+	<color name="cpp_selected_angle_unit_text">#ffffff99</color>
 	<color name="cpp_main_bg">#ff000000</color>
 	<color name="cpp_pane_background">#ff1f1f1f</color>
-	<color name="cpp_metro_button_background">#ff1f1f1f</color>
+	<color name="cpp_metro_button_dark">#ff000000</color>
+	<color name="cpp_metro_button">#212121</color>
+	<color name="cpp_metro_button_light">#393939</color>
 	<color name="cpp_metro_blue">#10648c</color>
 	<color name="cpp_metro_blue_dark">#ff092c39</color>
-	<color name="cpp_metro_green_color">#088e3a</color>
-	<color name="cpp_metro_purple_color">#651456</color>
-	<color name="cpp_metro_light_button_background">#393939</color>
-    <color name="cpp_widget_cursor_color">#ff707070</color>
-    <color name="cpp_text_primary">#ddffffff</color>
-    <color name="cpp_text_secondary">#89ffffff</color>
-    <color name="cpp_widget_ripple">#40ffffff</color>
+	<color name="cpp_metro_green">#088e3a</color>
+	<color name="cpp_metro_purple">#651456</color>
+	<color name="cpp_widget_cursor">#ff707070</color>
+	<color name="cpp_text_primary">#ddffffff</color>
+	<color name="cpp_text_secondary">#89ffffff</color>
+	<color name="cpp_widget_ripple">#40ffffff</color>
 </resources>
\ No newline at end of file
diff --git a/android-app/src/main/res/values/styles.xml b/android-app/src/main/res/values/styles.xml
index f9720b94..6a3dc5a3 100644
--- a/android-app/src/main/res/values/styles.xml
+++ b/android-app/src/main/res/values/styles.xml
@@ -46,7 +46,7 @@
 		<item name="android:focusable">true</item>
 		<item name="android:background">@drawable/metro_blue_button</item>
 		<item name="android:textSize">@dimen/cpp_button_text_size</item>
-		<item name="android:textColor">@color/cpp_button_text_color</item>
+		<item name="android:textColor">@color/cpp_button_text</item>
 	</style>
 
 	<style name="cpp_keyboard_button_style">
@@ -57,7 +57,7 @@
 		<item name="android:background">@drawable/metro_button_dark</item>
 		<item name="android:layout_margin">@dimen/cpp_button_margin</item>
 		<item name="android:textSize">@dimen/cpp_keyboard_button_text_size</item>
-		<item name="android:textColor">@color/cpp_button_text_color</item>
+		<item name="android:textColor">@color/cpp_button_text</item>
 		<item name="android:scaleType">centerInside</item>
 	</style>
 
@@ -103,7 +103,7 @@
 
 	<style name="cpp_default_text">
 		<item name="android:background">@android:color/transparent</item>
-		<item name="android:textColor">@color/cpp_default_text_color</item>
+		<item name="android:textColor">@color/cpp_text</item>
 	</style>
 
 
diff --git a/android-app/src/main/res/values/theme.xml b/android-app/src/main/res/values/theme.xml
new file mode 100644
index 00000000..c50fcf30
--- /dev/null
+++ b/android-app/src/main/res/values/theme.xml
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  ~ Copyright 2013 serso aka se.solovyev
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~    http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  ~
+  ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  ~ Contact details
+  ~
+  ~ Email: se.solovyev@gmail.com
+  ~ Site:  http://se.solovyev.org
+  -->
+
+<resources>
+
+	<style name="Theme" parent="Theme.Base"></style>
+	<style name="Theme.Dialog" parent="Theme.Base.Dialog"></style>
+
+	<style name="Theme.Base" parent="@style/Theme.AppCompat"></style>
+	<style name="Theme.Base.Dialog" parent="@style/Theme.AppCompat.Dialog"></style>
+
+</resources>
\ No newline at end of file
diff --git a/android-app/src/main/res/values/theme_gray.xml b/android-app/src/main/res/values/theme_gray.xml
index 36166b77..df637b03 100644
--- a/android-app/src/main/res/values/theme_gray.xml
+++ b/android-app/src/main/res/values/theme_gray.xml
@@ -40,7 +40,7 @@
 	</style>
 
 	<style name="cpp_default_operation_button_style" parent="cpp_default_digit_button_style">
-		<item name="android:textColor">@color/cpp_button_operator_text_color</item>
+		<item name="android:textColor">@color/cpp_button_text_operator</item>
 	</style>
 
 	<style name="cpp_default_control_image_button_style" parent="cpp_default_control_button_style">
@@ -115,7 +115,7 @@
 		<item name="android:layout_width">match_parent</item>
 	</style>
 
-	<style name="cpp_gray_theme" parent="@style/Theme.AppCompat">
+	<style name="cpp_gray_theme" parent="Theme">
 		<item name="android:windowBackground">@color/cpp_main_bg</item>
 
 		<!-- buttons -->
@@ -139,7 +139,7 @@
 		<item name="cpp_pane_style_transparent">@style/cpp_default_pane_style_transparent</item>
 	</style>
 
-	<style name="cpp_gray_dialog_theme" parent="@style/Theme.AppCompat.Dialog">
+	<style name="cpp_gray_dialog_theme" parent="Theme.Dialog">
 		<item name="android:windowCloseOnTouchOutside">false</item>
 		<!-- buttons -->
 		<item name="cpp_digit_button_style">@style/cpp_default_digit_button_style</item>
diff --git a/android-app/src/main/res/values/theme_light_blue.xml b/android-app/src/main/res/values/theme_light_blue.xml
index 60f3dedb..860b2a0b 100644
--- a/android-app/src/main/res/values/theme_light_blue.xml
+++ b/android-app/src/main/res/values/theme_light_blue.xml
@@ -31,7 +31,7 @@
 	</style>
 
 	<style name="light_blue_operation_button_style" parent="light_blue_digit_button_style">
-		<item name="android:textColor">@color/cpp_button_operator_text_color</item>
+		<item name="android:textColor">@color/cpp_button_text_operator</item>
 	</style>
 
 	<style name="light_blue_control_image_button_style" parent="light_blue_control_button_style">
diff --git a/android-app/src/main/res/values/theme_violet.xml b/android-app/src/main/res/values/theme_violet.xml
index dd0b9308..a414abbe 100644
--- a/android-app/src/main/res/values/theme_violet.xml
+++ b/android-app/src/main/res/values/theme_violet.xml
@@ -27,7 +27,7 @@
 	</style>
 
 	<style name="violet_operation_button_style" parent="violet_digit_button_style">
-		<item name="android:textColor">@color/cpp_button_operator_text_color</item>
+		<item name="android:textColor">@color/cpp_button_text_operator</item>
 	</style>
 
 	<style name="violet_control_button_style" parent="cpp_keyboard_button_style">