Use red-on-white rather than red-on-black.

Relying purely on color change is unfriendly to those of us that are
color blind; red on black is a particularly challenging
combination. (Even worse when working from home, since video
compression can lead to washed out colors.)

Changing from light on dark to dark on light should make it fairly
obvious even to those with monochrome vision.

Test: Manual
Change-Id: I79013686038cb4ebea6087b53cece3266bf6ec0b