Fixes #4229 Support transparent foreground/background in v2#4234

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tznind wants to merge 9 commits intogui-cs:v2_developfrom

tznind:transparent-backgrounds

Commits on Sep 1, 2025

Make black clear background color instead of force black
tznind
committed

Commits on Sep 5, 2025

Also require alpha to be 0 before using transparent background and make that default theme
tznind
committed
Implement for windows driver too and simplify
tznind
committed

Commits on Sep 6, 2025

- Make all StandardColor have correct A (255)
tznind
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Revert changes to 'special case' Transparent and instead make StandardColor uint so it can have FF for alpha on all values
tznind
committed