[Shasown]

There isnt wrong with you, de-oxygenated blood pools in the legs, as the skin cools the fresh bright blood that normally keeps your skin pink is prevented from moving through the subsurface capillaries to prevent over cooling the blood, this means that lower lying de-oxygenated blood is allowed to show through, this blood is darker in colour and looks blue/purple through the skin.

The purple hue should disappear after you warm up or start increasing the blood flow into and from the legs by exercising them.