Neptune 's blue color is much brighter compared to Uranus ' , which has a similar amount of methane , so there might be another reason why Neptune is blue . As with Uranus , this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue , although Neptune 's vivid azure differs from Uranus 's milder cyan . Since Neptune 's atmospheric methane content is similar to that of Uranus , some unknown atmospheric constituent is thought to contribute to Neptune 's color .