The Game Boy Color could display 4 different colors (there was an awful red and yellow palette...)
4 Colors, what's so hard to understand? Look at the pixels, if there's more than 4 color values you're doing it wrong
Look at the end of this talk to get "thy this is so hard" https://itch.io/jam/gbjam-5/topic/40657/how-is-this-working. Also don't assume that we all know how these gameboy things worked...