Force using only 16 colors

[makzsslm]

I might be a weirdo, but i don't like seeing many different colors all the time. To me, seeing two colors that are almost the same but not really is a papercut on good days, and triggering my OCD on bad days.
I've carefully chosen 16 I like and take time to make custom themes for each app. This can be time consuming.
It would be great if there was a way to solve this on a terminal level: for any given color, just assign the one that is the closest in RGB color space, using the palette in the config.
I get that this might conflict with TUIs for instance (no cool doom demo :/). Maybe there could be an option to limit it to non-"fullscreen".