http://www.nature.com/news/first-distant-planet-to-be-seen-in-colour-is-blue-1.13376
BLUE GAS GIANT By observing exoplanet HD 189733 b before, during and after it disappeared behind its host star, astronomers were able to discover that its colour is a deep blue.Image: Artist’s impression

From Nature magazine

A navy-blue world orbiting a faraway star is the first exoplanet to have its colour directly measured.

Discovered in 2005, HD 189733 b is one of the best-studied planets outside the Solar System, orbiting a star about 19 parsecs away in the Vulpecula, or Fox, constellation. Previous efforts to observe the planet focused on the infrared light it emits — invisible to the human eye.

Last December, astrophysicist Tom Evans at the University of Oxford, UK, and his colleagues used the Hubble Space Telescope to observe the planet and its host star. Hubble’s optical resolution is not high enough to actually ‘see’ the planet as a dot of light separate from its star, so instead, the telescope receives light from both objects that mix into a single point source. To isolate the light contribution of the planet, Evans and his colleagues waited for the planet to move behind the star during its orbit, so that its light would be blocked, and looked for changes in light colour.

via First Distant Planet to Be Seen in Color Is Blue [Video]: Scientific American.