Terminals should generate the 256-color palette

This is interesting. I'm not sure how well it would work in practice; most terminal programs seem to either work correctly with 16 colors, or force 24-bit colors. Of course, the things that don't reasonably work with 16 colors (LS_COLORS I am looking at you with rage) won't with 256, either.

I think this idea has merit! If a TUI wants to reproduce an exact colour, RGB modes exist: so I don't see a good reason to not thematically interpret the 256 colour mode in a similar way.