What does it meanif you have blue darrhea?

Blue: Most likely you ate something blue that did not agree with you.

Probably infection: Color of stool may change to greenish or bluish green due to effect of bile and its breakdown products after it passes through the intestines. Viral infections can make stool look bluish green as well from which it should return to normal in a couple of weeks.

Blue food: What comes in must come out - so what blue thing did you eat a lot of? If it's more reddish, then the concern is active bleeding in the gastrointestinal tract. If it is more blackish, this can be blood from recent or slow active source of bleeding. Please seek medical attention.