An automobile can be painted virtually any color that can be imagined. Water and latex paints interact poorly with metal, so the only limit is the color of automotive, or metal friendly, paint available.
Anybody can paint or repaint an automobile granted they have the correct equipment. However, unless one already has previous experience painting automobiles, it is recommended that all automobile paint jobs be referred to a professional who can ensure the highest quality and greatest craftsmanship. It is easier to paint an already light-colored automobile a darker color than it is to paint an already dark-colored automobile a lighter color.