This illustration shows HD 189733b, a huge gas giant that orbits very close to its host star HD 189733.
By observing this planet before, during, and after it disappeared behind its host star during orbit, astronomers were able to deduce that HD 189733b is a deep, azure blue — reminiscent of Earth’s colour as seen from space.
NASA, ESA, M. Kornmesser
CC BY 3.0
<a rel="nofollow" class="external text" href="http://spacetelescope.org/videos/heic1312a/">Blue planet HD 189733b around its host star (artist’s impression)</a>