Smart! - I am potty training my toddler who is also learning her colors. I had the idea to put in one of those toilet bowl cleaners that turn the water blue. Then, I showed her how our pee-pee (sorry, but everything at my house is about pee-pee and poo-poo right now!) turns the water GREEN. She loved it! (So did my four year old!) Sometimes she'll even say "I go make green, I go make green!"