app/src/main/res/layout/brush_color_item.xml
<?xml version="1.0" encoding="utf-8"?>
<Button xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/doodle_color"
android:layout_width="20dp"
android:layout_height="20dp"
android:layout_margin="3dp"
android:background="@color/red" />