Greyish-brown potatoes are still safe to eat but they aren’t as nice to look at. When cooking these discolored spuds, they tend to become a mushy mess too. The flesh of the potatoes start to change colors from oxidation once they’re cut and the starch gets exposed to oxygen.  Putting the potatoes in a bowl of cold water once you chop them will help stop oxidation and will pull some of the starch from the potatoes, giving them a crisper texture while cooking.