https://github.com/janvancoppenolle/LUT/tree/main/Retro%20GPU%20Conversion
A B C

MOS VIC-II (16 colours)

Used in the Commodore 64 and based on the colour palette described here: http://unusedino.de/ec64/technical/misc/vic656x/colors/index.html
  Nearest  
  Perceptual  

C64 (16 colours)

An alternative to the MOS VIC-II colour palette that is a bit more vivid.
  Nearest  
  Perceptual  

Apple II (15 colours)
  Nearest  
  Perceptual  

Texas Instruments TMS9918 (15 colours)
  Nearest  
  Perceptual  

IBM CGA (16 colours)
  Nearest  
  Perceptual  

4-bit RGBI (16 colours)
  Nearest  
  Perceptual  

ZX Spectrum (15 colours)
  Nearest  

BBC Micro (8 colours)
  Nearest  

References

https://en.wikipedia.org/wiki/List_of_8-bit_computer_hardware_graphics
https://en.wikipedia.org/wiki/List_of_monochrome_and_RGB_color_formats
http://unusedino.de/ec64/technical/misc/vic656x/colors/index.html
https://en.wikipedia.org/wiki/Texas_Instruments_TMS9918