Modify fast scroll alphabetical bubble

Question

I am trying to change the bubble containing the letter in the scrollbar.

What is its official name BTW ?

I am not talking about the fastScrollThumbDrawable or fastScrollTrackDrawable on the right side. See the image below.

1. How to change the color of this bubble ?

This answer uses colorAccent. But I don't want to affect the theme.

2. How to change the position of this bubble ?

The answer from Huby to How to handle the fast-scroller on Lollipop 5.1 gives a partial answer to the change the location of the bubble