There is a fascinating new page on the Mars Exploration Rover Pancam science team's website, full of color versions of Opportunity's microscopic images. The Microscopic Imager is one of the tools on the end of the robotic arm, and serves as a hand lens for the robot geologist to explore the rocks and sands of Mars in great detail. But the Microscopic Imager is a black-and-white one, without the filters necessary to create color views. Amateurs and professionals both have occasionally added color to Microscopic Imager pictures by warping and overlaying color images from the rovers' Pancams, but this was done on a one-by-one basis. Now, though, it seems that the lead for the rovers' Microscopic Imager science team, Ken Herkenhoff, is producing these color Pancam overlays onto Microscopic Imager photos in a systematic way.
Here's just one example, from way back, when Opportunity was still in Eagle crater, where she landed. You can readily see where the Microscopic Imager coverage ends; its square field of view is 31 millimeters on a side.
These images are at a resolution of 30 micrometers per pixel. The berries in the image above are between 3 and 4 millimeters across. Apart from their scientific interest, I find these pictures to be aesthetically beautiful and so different from most of the space images that we customarily look at, which are taken from so much farther away. Whenever I go out on a field trip and see an interesting rock, one of the first things I do is to put my nose right up to it and see what crystal shapes I can find, what colors they are, how they are put together. The Microscopic Imager lets us do that, but in black and white; adding in the Pancam color adds a whole new layer of verisimilitude to the experience of seeing these ultra-closeup shots from Mars.