Integumentary System

Te GWS does not have scales like other fish. Its skin is made up of thousands of microscopic denticles. They all lie flat along its body with the point towards its tail. This arrangement ensures that the shark's body is streamlined. If you were to run your hand along the skin in the nose-to-tail direction the skin would feel smooth as silk; if, however, you were to rub it in the opposite direction, from tail to nose, the denticles would be raised upwards making the skin feel like sandpaper.
Most great whites are not a pure white like the name implies. All white sharks have a pale underbelly while the top half is dark. The actual color can vary depending on the region it comes from. For instance, Californian sharks are a very dark slate-grey, almost black, while South African sharks often appear to be dun or olive-colored as well as Australian great whites.

http://videos.howstuffworks.com/discovery/6934-shark-week-shark-skin-vs-sandpaper-video.htm
This video shows relative shark skin is to sand paper