Provide a way to unset color

[MiSawa]

Problem
I'd like to use a builtin theme, catppuccin, except I'd like the background to be unset (which results in transparent in my terminal emulator), but there doesn't seem to be a way to override a color with none.

[ui]
theme = "catppuccin"
[ui.theme_overrides]
background = "..." # How to disable background??

Feature
Introduce a (pseudo) color name "none" (or maybe the empty string) to represent the terminal default fg/bg color. The specified element should be shown in the terminal's default color, as if no color was specified.

Examples

[ui]
theme = "catppuccin"
[ui.theme_overrides]
background = "none"