Why does my diarrhea change colors?

Been eating old food from the back of the fridge and having some good diarrhea lately. Very soupy, virtually no solids, it's great stuff. I've had a harmonious relationship with my bowels for the most part. However, when it's in the toilet bowl it rapidly changes colors - pastels, neons, the whole spectrum. I like to observe my diarrhea for a while before flushing it, but the color changing really annoys me. I'm used to worshiping the burnt siennas, the hyper-khakis, the bright tans and the fluorescent beiges, but I don't have the means to worship these bright colors.