What colour is Uranus?

Short answer: Blue-green.

Long answer: Uranus is a gas giant planet, made up mostly of hydrogen (83%), helium (15%) and methane (2.3%). Although methane is only a small fraction of the overall atmospheric composition, it is responsible for Uranus' blue-green colour. Methane absorbs the red part of the light from the sun and reflects the blue light. This makes Uranus look blue/green.