Merge pull request getodk#2902 from zestyping/ping/tintmode

Use our themes to fix the default tintMode to SRC_IN.

collect_app/src/main/res/values/theme.xml

@@ -27,6 +27,15 @@
         <item name="android:textDirection" tools:targetApi="17">locale</item>
         <item name="warningColor">@color/red_500</item>
         <item name="dividerCompat">@android:drawable/divider_horizontal_dark</item>
+        <!--
+            The default tint mode for ImageViews is SRC_ATOP, which produces
+            incorrect blending results when tinting images with a colour that
+            has an alpha channel (for example, the alpha channel is used to
+            turn disabled buttons grey).  The correct tint mode is SRC_IN,
+            which is the default tint mode in Android everywhere else.  See:
+            https://developer.android.com/reference/android/widget/ImageView.html#attr_android:tint
+        -->
+        <item name="android:tintMode" tools:targetApi="21">src_in</item>
     </style>
 
     <style name="AppTheme.SettingsTheme.Dark" parent="BaseDarkAppTheme">
@@ -70,6 +79,7 @@
         <item name="android:textDirection" tools:targetApi="17">locale</item>
         <item name="warningColor">@color/red_500</item>
         <item name="dividerCompat">@android:drawable/divider_horizontal_bright</item>
+        <item name="android:tintMode" tools:targetApi="21">src_in</item>
     </style>
 
     <style name="AlertDialogTheme.Light" parent="Theme.AppCompat.Light.Dialog.Alert">