GRC colorization

I noticed that some text background washout happens with commands colorized by grc.

Ghostty's default is ok, but some themes like catppuccin make text with background color blocking really hard to read.

Default:

Catppuccin:

Reproduce the washout with commands colorized by grc using Ghostty's default theme and the catppuccin theme, referring to the screenshots in the issue. Inspect the theme definitions to determine which background-color treatment affects readability; done means colorized output remains clearly readable without losing the intended palette.

Written by the indexing model from the issue text.