yellow spit up?

Sh
My 3 month old just spit up and some of it was yellow!!! I'm calling pedi but has that happened to anyone? She's mainly breastfed but she ate formula last night because I was having a few alcoholic beverages. I don't think that would have anything to do with it though. She seems totally normal and fine. No fever. And she spit up again after that and it was normal.