Approximately 7,345. http://wiki.answers.com/Q/How_many_hippos_does_it_take_to_turn_the_color_green_to_purple
The Internet Oracle has pondered your question deeply. Your question was: > Oh Oracle most wise, > > Why does the sun lighten our hair, but darkens our skin? And in response, thus spake the Oracle: } The darkness to the skin has to come from somewhere! Through a complex } process, the sunlight shifts the dark from the hair to the surface of } the skin. This is why really light blonde people don't tan, but burn. } They have no dark to move.