Let me play Devil's Advocate and ask how you know that Nick's image is actually correct? (I discount my images because I wasn't trying to get the colors right, just doing a straight RGB combination.)

I know that Earthlike color schemes appeal to us instinctively. But how much weight should science give to instinct? Isn't it appropriate to give more weight to the arguments of experts who can refer to a rich body of experience and build a formal structure of self-consistent logic?

Intuition doesn't tell us that the Earth is a sphere when we look at the horizon--intuition tells us we live on a flat plane and we'll fall off if we go beyond the horizon. Science can produce counterintuitive results and prove them.

That's not to say intuition's worthless. When I look at those dayglo Mordor images my instincts tell me something's wrong, which motivates my left brain to try and figure it out. Those "vibrant" deeply-saturated colors could only be produced if the atmosphere were loaded with dust, and a single kind of dust which passes a relatively narrow part of the spectrum. Orbital images show the atmosphere above the landing sites (and above most of Mars most of the time) to be pretty much clear. Spirt and Opportunity didn't land in the middle of dust storms.

An atmosphere of clear carbon dioxide will be blue according to Rayleigh scattering. Any other color will be the result of "contamination" by dust. So I'd expect the sky to be usually a dark but unsaturated blue (Mars gets less than 50% of the sunshine of Earth). When the wind kicks up (a pretty wimpy wind, given the thin atmosphere) the color will shift toward a color consistent with the material suspended in the atmosphere. Sometimes that will be red dust, but since we see other colors on Mars, it could well be oranges, yellows, greys, and even green.

A flaw I see in the argument that the atmosphere of Mars must be reddish because there must be a lot of dust in the air is based on a comparison with Earth. Our sky is generally blue, yet our planet has a thicker atmosphere better able than Mars to kick up and suspend dust for long periods of time; it gets more solar radiation to pump energy into a thicker atmosphere and keep it roiled. Why isn't Earth's sky usually red, orange, grey, or green? Why is it usually blue?

Those are the arguments to back up my intuition: It beggars the imagination to think that the atmosphere at every landing site is laden with red dust when in general the atmosphere of Mars looks clear and clean most of the time. Mars isn't Earth, yet it's not so alien that it isn't subject to the same physical laws as Earth.

Nevada's soil is generally reddish, there's little vegetation to hold it down, and the winds can get pretty fierce. Yet the sky is blue every time I visit (except last month, when it clouded over and snowed).

The history of the Vikings and Pathfinder will repeat itself. The Official Image Processing Experts will work over the MER images for a few months, then quietly release the results with a press release that says "ya know, after careful consideration, we think Mars looks a lot like Nevada".

You heard it here first.

Again.