Final answer:
The blue-green color of planets like Uranus and Neptune is due to the scattering of sunlight by methane in their atmospheres, which absorbs red light and scatters blue light more efficiently.
Step-by-step explanation:
The appearance of planets as blue-green is often due to the scattering of sunlight by the atmospheric composition of the planet. In the case of the ice giants in our solar system, Uranus and Neptune, their distinctive blue color is primarily due to methane ice clouds in their atmospheres. When sunlight reflects off these planets, methane absorbs red light which allows blue light to be scattered more efficiently in the atmosphere, giving these planets their blue-green tint. Moreover, the scattering of sunlight is what makes the Earth's sky appear blue since gases in our atmosphere scatter the blue component of sunlight more than other colors.