Thanks for stopping by and giving feedback :) Difference in color is calculated by RGB values, so it can be tricky for human eye to determine which ones are different. It's design flaw, but there is no proper way around it. Still, we hope that game is somewhat fun.  As for cover, it's drawn by my only teammate, Mihailo, in under one hour mark. He also did in-game art. You can check his other stuff on https://www.behance.net/AcidRaja.