Harris Teeter has these vividly colored cupcakes. I surmised that if you ate several (3+) of them, it would turn your poop colors. I had noticed this before, but was uncertain if the cupcakes were the source. So, I did not eat for 24 hours before the cupcakes. I ate 6 cupcakes (vivid blue) and this was the result. If you do not see them for sale, they will make them for you.
This morning I saw the results of an experiment I performed. The turd was a vivid green color. It was an average size and had a slightly sweet smell to it, like burning sugar. It came out with ease and clean up was no problem. I rate this a 10, for the coolness factor.