My dog has purple skin...why?

My dog Maxwell had surgery for his femur about two months ago. He had his pin removed last month and is doing great. He was in a couple weeks ago to get his stitches and staples out of his leg. They had shaved the area a few times. Recently he has a purple tint to this area of his skin. He doesnt act any differently or care if you touch it. He is completely normal. I was just wondering if it could be a potential problem or if it is just nothing. I will call the vet tomorrow...i just need some opinions on it.