While hairlessness in cats is a naturally occurring genetic mutation, the Sphynx breed was originally developed through selective breeding.
A Sphynx cat's skin is the color of what the fur would be, if it were present. They can be any of the colors and patterns exhibited in a typical cat. This includes tabby, solid, pointed, calico, etc.
The Sphynx mutation produces a structural damage of the hair. If any hair is present it can easily be removed.