Fix contrast of monochrome fixed colors

Screenshots:
https://screenshot.googleplex.com/4ddevTXDQpRwWPA https://screenshot.googleplex.com/8T4HVfrHHsR9cSD
https://screenshot.googleplex.com/7Wp7k5njCE33n3z
https://screenshot.googleplex.com/7Np6gEXU7utJFsm

Bug: 282951509
Test: atest SystemPaletteTest
Change-Id: I678aea8a09c7b9cf30b437f15c4518415e3de319
1 file changed