Could be breast cancer. My aunt had this and they didn't find a tumor but cancer on her skin.
it looks like a really bad bruise...
Do u mean the color under your nipple is yellow? or discharge coming from nipple, either way you will want to make an appoinment with your doctor these could be some signs of breast cancer, Im not sure but i did a report on Breast cancer this semester for Biology and discoloration and or discharge requires medical attention . make appointment ASAP to make sure. or call your GYN's nurse.