Add Color Desaturation/Filter Option For GBC Games

[johnnywagner]

I realize this project is a bit dead these days but thought I'd leave this suggestion here: Color de-saturation/modulation filters have become common among GBC emulators these days to emulate how the games looked on the original reflective LCDs, even making it into the official Nintendo Switch online emulators. It's a pretty simple feature from what I understand (depending on how accurate you want to get) & I'd love to see the option come to GameYob one day.

Example photo of some games being desaturated/altered on the right: