Did the exact same thing for way too long. I had like six colors going and spent more time picking which one to use than actually reading the stuff I was marking. Then one day I went back to review and couldn't remember why half of it was yellow vs pink vs green. Total waste. The only thing that ever helped me was writing short notes in the margin with my own words. That actually sticks because you have to think about it instead of just dragging a neon streak across the page.