Use lookup key to determine the letter tile color

The lookup key is part of the lookup URI that is supposed to be stable even if the row is moved around.

TEST=TAP
Bug: 78266240
Test: TAP
PiperOrigin-RevId: 197822055
Change-Id: Iee09556c284efaa68f71e1e0a69a511944c6b46e
1 file changed