What could cause a whitish-green stool? Earlier I passed a whitish-green stool and in the same movement had normal brown stool. What's going on?

What you ate,, Whatever you ate is the likely cause of your abnormal colored stool. Sometimes if you had a lot of vegetables or fatty foods, it changes the way your stool looks. Fatty foods can make it look lighter in color while red meat may make it darker. Different vegetables can make it look greener. Without any health issues and being that you're young it's likely ok. See your dr. If still concerned.