That’s a no-no, you need to discard the potatoes.  It’s fitting that I received this question on Earth Day, April 22^nd 2016 because it is a perfect reminder that potatoes are one of those crops that grow in dirt. Those that are not harvested and immediately sent to market are placed in storage. Idaho potato farmers take the potatoes out of storage at typically 45-48°F and send them off to a potato shipper who has machinery to wash and sort and grade, along with human eyes help. They are kept at warmer room temps, but not cooked.

Once cooked and left out at room temp, here is the issue… holding hot food needs to be 135°F or above and holding cold food should be at 41°F or below. Since your potatoes were boiled, the proper steps are to cool to 70°F within two hours and then to place in refrigeration to cool down to 41°F.

Issues could occur for example if someone peeled the potato with a small cut on their hands, or if the potatoes were left uncovered as something or even a fly could drop into the container. While the potato, with skin on, might be less prone to the food safety issues if it still had any pathogens in the dirt after washing and boiling, leaving out at room temp is not good. Often, peeled potato that has been cooked will turn gray from exposure to air, accelerated when left out at room temp.