Many species of sharks that hunt and feed near the surface are "counter shaded". That is they have white bellies which makes them harder to see if you are below them and looking up and they have dark backs which makes them harder to see if you are looking down on them. It is suggested that the pattern of light dots and lines on a whale sharks back resemble a school of fish or reflections of the sun on a shallow reef. You will notice that spotted eagle rays have also evolved a similar camouflage patterning.