evidence: The theory, which was discussed on the podcast "Incomeparent," revolves around the concept that the colors found on different toothpaste tubes contain clues about the ingredients hiding within. [...] You may have noticed that whenever you purchase a tube of toothpaste, there is a small colored bar at the bottom. The colors are usually green, blue, red, and black. Per the theory, the color of the bar reveals the toothpaste's formulation. [...] If you want to be extra safe and know exactly what your toothpaste is made of, the ingredients are usually printed on the tube itself or the package it came in.