Adding minimal customizable background colour support.

This adds back minimal support from
https://googleplex-android-review.googlesource.com/#/c/1442940/1
because the bigger thing had to be reverted.

Bug: 31459804
Change-Id: I545d1f7639c9dada417e95b5da6290414d3de05d
(cherry picked from commit d64a1582)