Neptune's atmosphere extends about 4,600 miles (7,400 km) above the mantle. It is 87 percent hydrogen, 12 percent helium, and 0.5 percent methane. In the middle levels of the atmosphere are dark clouds of hydrogen sulfide. Above these clouds is a thick layer of blue clouds. This layer is made of methane gas. White clouds made of methane crystals drift above the blue cloud deck. Above this is a haze of hydrocarbons.
The main cloud deck is blue because it is made of methane. Methane absorbs red and yellow light. It reflects blue light. The light reflected from this layer gives the planet its bluish color.
