Bouncer - Update selected item text color

Constrast was too low, didn't match specs. Also noticed that if the
user updated the dark mode while on lockscreen, the colors for both
the user switcher and the num pad keys were not properly updating.

Fixes: 221368641
Test: manual
Change-Id: I5b9b2dca8f8246d403bcf919b8f2a2ba4ea2d9ec
(cherry picked from commit 195baa1c)