What Color is the Sky ... on Your Planet?

Ever wonder whether the technicolor planets in science fiction universes like Star Trek have any basis on reality? Maybe a thought experiment could lead the way to an answer.

Much of Earth is forested and much of it is desert. Even so, however, the Earth appears primarily blue with white swirls because two-thirds of it is covered by water. The browns of the land areas are comparatively muted.

Star Trek has its share of multicolored planets, sometimes of colors seemingly implausible to the modern eye. How likely, for example, is a purplish planet to exist? Perhaps more likely than one would think. If the planet in an episode had only a very small proportion of land to sea ratio, and if the atmosphere or oceans were purplish, then the planet as a whole could be more or less purple when viewed from space.

The planets in our own Solar System have a diversity of colors when viewed from space. Mercury is dark grey, Venus is white (from the cloud cover), the Earth is blue-and-white, Mars is ochre, Jupiter is striped brown, Saturn is tannish, Uranus is a pastel blue, and Neptune is a deep blue. Poor, demoted Pluto (now considered a dwarf planet) is apparently pinkish, as seen in this disco ball-like mosaic of its surface:

http://upload.wikimedia.org/wikipedia/en/3/30/Pluto.jpg