Erythrism is a color pigment mutation that causes unusual reddish pigmentation all over the centaurs body. It affects skin,coat, keratin parts like nails, claws and hooves. 

Erythrism affects centaurs eyes as well, making them always appear with warm undertones and reddish, such as: browns, oranges, reds, peach, etc. 

When designing an erythrism affected centaur, you can either use a slider offered below, or freehand the colors. The main point that the centaurs coloration matches the mutations description.