What to do with dehydrated potatoes tainted black? I had many potatoes I wanted to preserve for a long time. Usually the potatoes I keep in my kitchen get rotten after a month or two (and I don't have a cellar to keep them cool), I decided to dehydrate them. So I grinded them in a food-processor and put in a food-dehydrator in 65 Celsius. After several hours they became dry but also got colored black - a strong black color on the (previously) white potatoes and a weaker color on the red potatoes.

Is there anything useful I can cook with these potatoes that turned black?
Throw them away. I would not expect potatoes to go black in the dehydration process, and although they may be safe to eat I would not expect them to be palatable, or inviting in any way. You cannot be sure they aren't toxic, and you wouldn't put them on a guest's plate, so chuck them.