Here is a small gallery of Jupiter's moons shown in colors that approximate their actual appearance. We have brightened the violet images to better represent the satellites' surfaces in blue light, but the effect is scarcely noticable because of the yellowish tinge of all of the moons (partly due to contamination from Io, a notorious source of "second-hand smoke" in the Jupiter system). Click on any of the pictures to retrieve a full size image.
Io:
"Io True Color Orbit 2" 
"Io True Color Orbit 14"
Both of these pictures of Io have Jupiter in the background, out of focus
because the camera was tracking the moon instead of the planet. These two
pictures look a little different because of changes in illumination: on
orbit 2, Galileo saw a full moon with the sun directly behind the
spacecraft. On orbit 14, the sun shone obliquely onto the surface.The
picture on the right is actually two images put together into a "mosaic".
The colored stripes across the mosaic are caused by missing data.
Europa:
"Europa True Color Orbit 1" 
"Europa True Color Orbit 14" The following pictures were all taken at sunrise, so they appear darker than those above:
"Europa True Color Orbit 19"
Ganymede:
"Ganymede True Color Orbit 1" This is the only true color image of Ganymede acquired by Galileo. The gap at the bottom is due to missing red filter data.
Callisto:
"Callisto True Color Orbit 20"
"Callisto Brightened True Color Orbit 20"
This image was also taken near dawn, so we've brightened it up for you without altering the color balence. The green column near the middle is due to a pixel on the detector that was damaged by radiation.
Hmm, they look awfully drab in comparison to the Galileo pictures I've seen on the web!