Someone posted this on the Uplink.space.com bbs:

"I just saw the 4/1 press briefing thanks to SAIDias' press briefing archive http://mars.systemsfirst.com. About the 23rd minute a color image of a RAT hole in the rock Mazatzal is shown. It is explained that the image was obtained by the US Geological Survey in Flagstaff by combining information from microscopic images taken with and without the dust cover. The microscopic imager has no filters, like the Pan Cam, to use in producing color images but the dust cover has an orange tint (I guess it acts like a combination red/yellow filter). I went back to the Spirit raw images and found that it has taken microscopic images with the dust cover closed before, presumably to produce color images. The first time was on sol 17. Typically, there are a series of several shots of the same patch of rock or ground, the last being taken with the dust cover closed. These images are in fact hardly distinguishable from those taken with the dust cover open."

They might not be distinguishable in the B/W images but perhaps they could be combined to produce color images as with the image of Mazatzal.

Bob Clark