yellow bruise from pumping?

So I just noticed I have a yellowish looking bruise like spit on my left breast. I am exclusively pumping since my baby had trouble latching. Some people said it could be from the pump but it is off to the side and not really near the nipple. It doesn't hurt, but I'm a little worried. I haven't been on a good consistent pumping schedule so worried it might be mastitis. Has anyone had any experience with this symptom? Would love to hear what you did! Thanks!