Potatoes discolor for one of several reasons: When the potato has been bruised, or if the fresh peeled or cut potatoes are exposed to air for very long (usually 15 minutes or less) they begin to oxidize. The potato turns a slight gray color and that color intensifies if left unattended – thus the reason to peel and/or cut potatoes directly into clean water, be that a pan or other kind of holding receptacle. The potatoes in the water will further benefit with the addition of the citric acid (lemon/lime juice) or vinegar, fresh or par-cooked as you describe. This helps in keeping the potatoes from discoloration.

Another reason potatoes may discolor is when they are held too cold (below 42° F) for too long of a period. When this occurs the starches within the potatoes convert to sugar, making for an overly-sweet potato and changing the cooking characteristics – thus the possibility of the potatoes discoloring.

Here are some links to test and recondition the potatoes, should they become so-affected:

https://idahopotato.com/dr-potato/my-potatoes-are-to-sweet-what-do-i-do

https://idahopotato.com/dr-potato/why-are-my-potatoes-discolored-after-cooking

Learn more about All Things Potato Salad here!