A callback to fetch a custom palette override color for colorIndex.
Custom palette colors override colors from the font's selected color palette.
It is not necessary to override all palette entries; return undefined for
entries that should be taken from the font palette.
This function might be called multiple times, but the custom palette is
expected to remain unchanged for the duration of one Font.paintGlyph
call.
A callback to fetch a custom palette override color for
colorIndex.Custom palette colors override colors from the font's selected color palette. It is not necessary to override all palette entries; return
undefinedfor entries that should be taken from the font palette.This function might be called multiple times, but the custom palette is expected to remain unchanged for the duration of one Font.paintGlyph call.