[zzo38computer]

If I make a terminal emulator, I would probably not support true colours in text but only in pictures (and it would be possible to disable pictures). I probably would not implement 256-colours either, because I agree with you; the user configures their own colours to use, and the terminal should use them. For text, only sixteen colours can be used.

Similarly, the user can also set their own fonts for the terminal, just as you can with colours and other functions. (However, some programs will have a reason to configure the fonts and palettes for the specific use, although most won't and even if they do the user might disable those features.)

A program can have an option (possibly by environment variable) to disable colours entirely; this might be necessary even if you can disable colours in the terminal emulator, because a program might want to use such things as reverse video, underlined text, etc to indicate some things when colours are disabled. (Disabled colours can also be useful if you do not have a colour display or if you want to print out a screenshot without a colour printer.)