Io in True Color . ... Credit Copyright: Galileo Project , JPL , NASA Explanation: The strangest moon in the Solar System is bright yellow. This recently released picture , showing Io's true colors, was taken in July by the Galileo spacecraft currently orbiting Jupiter. Io's colors derive from sulfur and molten silicate rock . The unusual surface of Io is kept very young by its system of active volcanoes . ... NASA Web Site Statements, Warnings, and Disclaimers . ...