This is due to spasm of the small arteries (known as arterioles) in the peripheries which causes a reduction of blood supply to the peripheries such as the fingers and toes, and also at times ears and nose. This results in first purplish discolouration and then whitening of the affected digits, returning to bright red once the circulation has been restored. It can affect one digit, or it can affect several. It can last anywhere from minutes to weeks, depending on how severe the disease is.
This means that normal skin will look normal, and then suddenly the affected skin will be white or purple.