Slightly greenish discharge. Maybe a darker yellow?

I am 27 ive been on birth control Yaz for 10 years now. For the past 2 years I would say I sometimes will get very thick discharge with a slight tint of green or a darker yellow?? I have been to the gyno for this issue like 3 times now over the course of those 2 years my tests always come back negative for std. Also come back negative for yeast infection and BV. I am stumped and I hate going to the gyno every couple of months because I get this on occasion. There is no smell to it at all. Has anyone had this issue and figured out what it could be? I am super confused and stumped on this. Could it be a PH issue?