Thanks for your question. There are a few thoughts and ideas that come to mind, but you will need to discuss this more with your doctor
. Like all body parts, the legs are supplied with blood via arteries, and the blood drains back to the heart via the veins, after delivering oxygen and nutrients and removing waste products from the cells. The veins of the legs have valves, which keep blood flowing towards the heart. The return of blood is facilitated by the pumping of muscles, which work to squeeze the veins and milk the blood back towards the heart. The first thing that seems to be possible is based on an understanding of what usually turns the skin purple. In general, a purple hue to the skin is caused by blood that has very little oxygen content. This is usually venous blood, which is on its way back to the heart. It is plausible that after a long day of exercise and effort your blood may tend to pool in your lower extremities a bit more due to a decreased action of pumping by your muscles. Microtrauma is another possibility, but seems less likely if it happens and heals each day. Other conditions, including some autoimmune conditions are possible. Please speak with your doctor about this condition.