On Android, you can adjust colors when an element receives focus. However, it's not possible to change the focus indicator of assistive technologies. Users can adjust their preferences in the system settings of Android.
You can use a ColorStateList to change colors based on the element state. An element moves into the state_focused whenever it receives focus.
The code sample below shows how to change the background color of a button on focus.
<!-- selector.xml -->
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@color/focused" android:state_focused="true" />
<item android:drawable="@color/default" />
</selector>
<!-- layout.xml -->
<Button
android:id="@+id/button"
android:background="@drawable/selector">
</Button>