When i sit down or stand up in the same position my toes turn purple. when i walk they turn back to the normal colour. i do not have any pain or tingling in my feet. what could be the reason for this?

Good observation! When you stand the pressure in you veins increases as much as 2 mm Hg per inch your toes are below your heart (hydrostatic pressure). So, if 60 inches, the pressure in you veins may go up to 120 mm Hg. Blood pools in your toes and desaturates and becomes purple. Walking squeezes blood out of your veins as they contract and,if valves are working, new, redder blood comes. Toes pink