Filter to dither to color palettes?

I recently saw an interesting horror game on itch .io that used an filter/post process to dither the colors on screen to 5 different shades of green, like old game boy games.

I believe that this game is using Unity.
Is there a filter like this for the BGE that anyone knows about?


Thanks, that looks like what I need. One question though, is there any way to remove the “grid” effect so that I get something like this?