After our son was potty trained, I wanted to encourage as much bathroom independence as possible, from managing his clothes to washing his hands. However, around that time, he forgot his right from his left and got really nervous that he'd turn on the hot water by mistake. (Our hot water is not hot enough for him to burn himself, but he was still nervous!) So, I put a green rubber band around the cold faucet and a red rubber band around the hot faucet. He knew green for "go" and red for "stop," of course! After that, he could wash his hands alone and made great strides toward not needing me in the bathroom.
Does anyone have an idea for doing this on a faucet that has just one handle? :)