The most volcanic world we know. Io is the most volcanic world we know, with hundreds of active volcanoes, kept hot by Jupiter squeezing it on every trip round. Its yellows and reds are sulphur.
A colour mosaic from Galileo, which circled Jupiter from 1995 to 2003, with Voyager 1’s pictures from 1979 filling in the side Galileo saw least.
USGS Astrogeology, Galileo and Voyager colour mosaic, public domain.