M*A*S*H - Derby Day Cake
During this episode, Margaret was arguing with a patient about the icing on the Derby Day cake. Margaret wanted lime, but the patient said, he "refused to put lime icing on a chocolate cake." However, at the end, when they brought the cake to Colonel Potter's office and he says, "This is leftover derby," you can see the cake is yellow, not chocolate
Episode "Potter's Retirement"