Fixed contrast with sfps overlay.

Tested various different themes

1. Choose a color in settings > wallpapers > basic colors
2. Go through enrollment
3. Verify that light/dark theme have appropriate contrast.

Test: Manually verified the contrast works for light/dark themes and
various different basic color styles.
Fixes: 243008680

Change-Id: I63900a8df21a3fe0f02e5da0db6e3b75520fce12