What Causes Bruising In Both The Legs From Below The Knee?

I've been on 60mg of prednisone daily for several weeks. I was slowly weaned down to 10 mg having taken my final dose last Wednesday. (I have colitis). 6 days ago I noticed bruising on both legs, from the knees down. No pain, just dicoloratoon. I'm s slim 5'7" 120 lbs and am fairly active, non smoker, non drinker 50 year old female