I have seen that it is possible to do, changing values in the memory with poke, but it's too "complex" for my need.
Maybe future versions can have the "color" parameter on font function (or something like pal function of pico-8).
As a veteran programmer who half the lifetime practised coding in BASIC and experimenting with writing games for nearly 40 years, I have worked with "poke" and "peek" years ago. But I warn you - manipulating bits to do custom font work with poke in font memory is tricky! The manipulated bits in the data bytes to assign to the TIC-80 memory addresses starting at 14604 in hexadecimal works the 8 binary digits in a byte from left to right: bit 1 is on the left and bit 7 is on the right.