Hmm, I thought you could just rename it to have a .gbc extension and the emulator would simulate color as if you had put an actual regular Game Boy cartridge in a Game Boy Color. I could’ve sworn I’ve done that with another emulator(s).
Alright, I see now that I need to enable this feature using “gb_colorization = enabled” for the Gambette emulator/librettogbc implementation.
Edit: Well, adding gb_colorization = enabled or gb_colorization = true in /opt/retropie/configs/gbc/retroarch.cfg doesn’t seem to work.