What Causes Purplish Vaginal Discharge?

Hi I went to the bathroom tonight and found a purple/pink discharge on my underwear , I am due to start ovulating tomorrow or maybe I have already been , I don t know , it was only one bit , I just thought it was a strange colour , but me and my partner are having unprotected sex in the hopes of maybe having a baby some time , I just don t know what this means ,