Colours of the planets of our solar system are determined by the way their surfaces reflect sunlight.
This may vary a lot due to the composition of the atmosphere, a rocky surface, or a lack of a rocky surface.
In this article, you will see a lot of similarities in the structures of Terrestrial(Rocky) and Jovian(Gaseous) planets. Mercury, Venus, Mars, and Earth are rocky planets. Therefore their colors are mostly determined by the materials on the solid surface.
Colours of gas giants are determined by the composition of their atmospheres. These planets are Jupiter, Saturn, Uranus, and Neptune.