NASA Hubble Finds a True Blue Planet

Astronomers making visible-light observations with NASA's Hubble Space Telescope have deduced the actual color of a planet orbiting another star 63 light-years away.
The planet is HD 189733b, one of the closest exoplanets that can be seen crossing the face of its star.
Hubble's Space Telescope Imaging Spectrograph measured changes in the color of light from the planet before, during and after a pass behind its star. There was a small drop in light and a slight change in the color of the light. "We saw the light becoming less bright in the blue but not in the green or red. Light was missing in the blue but not in the red when it was hidden," said research team member Frederic Pont of the University of Exeter in South West England. "This means that the object that disappeared was blue."