My rats pooped BLUE?!?

Hi. I noticed today that in my rat cage, there were a bunch of bright blue (like, cerulean blue) droppings on the bedding floor. I was absolutely shocked because the color was so bright and also because I don't recall ever feeding them anything that color. They do chew on these mineral candy chews that are pastel colors, but not really the same color as their poop. I'm very worried because I hear that rats poop blue when they've ingested rat poisoning. Does anyone know anything about rats pooping blue?