Similar substances are also fed to red canaries to achieve their red color. In the wild, birds such as Flamingoes get the same substances in the foods they eat. A flamingo that is kept in captivity and not fed any carotenoids (canthaxanthin powder is the one most often used with birds), it will turn white! Canthaxanthin, astaxanthin, etc, are carotenoids. It definitely could cause reddening of the snake's feces if the food the snake ate, contains carotenoids.
Carotenoid - Wikipedia, the free encyclopedia