One of the biggest obstacles when making Kartoffelklösse is keeping them from turning gray. This is caused by oxidation and is normal. As I said before, the color has no effect on the taste. My sister swears that stainless steel cookware, ice, ice cold water and lemon juice is the best answer. I have tried this method but sooner or later they begin changing color. It should also be noted that left-over Kartoffelklösse the next morning are dark gray, on the verge of turning black. Sliced and cooked in butter they soon turn back to white. Go figure! Once you've tried left-over Kartoffelklösse with eggs for breakfast you'll never be satisfied with hash browns again. During my research a combination of vinegar and a small amount of citric acid is suppose to do the trick. I want this to be as natural as possible and not effect or change the taste. If anyone reading this has the answer please let me know.