Greetings, welcome to the Forums.
Most of the leaves on your Peace Lily (Spathiphyllum cv.) look fine, but the one in the front is turning grey while still remaining glossy.
That is unusual. This might be just a freakish leaf, or their could be a cultural or pest issue involved. Examine that leaf above and below with a hand-lens to see if you notice any minite insects. If no actual sign of a pest is seen, just wait and observe for now. Will that leaf begin to die or will other leaves
Also tell me more about the care you Peace Lily gets. I think I see a brownish tip on one of the leaves in the back. Again, an occasional necrotic tip is nothing to worry too much about. This happens, but if it becomes a constant problem, re-examine the watering regime.
Also, in my experience, Spathiphyllum are unusually sensitive to excess fertilizer. Fertilize them sparingly.