Allow the app developer to set the background color of these components from the fragment layout XML. - [ ] Add `backgroundColor` on [`FlyoutFragment`](https://github.com/google/blockly-android/blob/develop/blocklylib-core/src/main/java/com/google/blockly/android/FlyoutFragment.java) - [ ] Add `backgroundColor` on [`CategorySelectorFragment`](https://github.com/google/blockly-android/blob/develop/blocklylib-core/src/main/java/com/google/blockly/android/CategorySelectorFragment.java) See [forum discussion](https://groups.google.com/d/msg/blockly/CvcHpS5v9bA/lrgZRGoiAwAJ).
Allow the app developer to set the background color of these components from the fragment layout XML.
backgroundColoronFlyoutFragmentbackgroundColoronCategorySelectorFragmentSee forum discussion.