ロストカラーズ

This is a world without colors - the world of lost colors. The main character is an executioner specializing in eliminating those infected by resurgences of color -- the so-called Colors. However, one day he becomes such being himself - and thus the hunter becomes the hunted. He needs to travel the colored world to uncover the mystery behind world creation and revert the disease of colors that he contracted. [Edited from vndbreview]