"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)."

You're right, a purely CO2 atmosphere on Mars without any dust would also be blue. As you said Rayleigh scattering (photons interacting with molecules) is the cause of this. Rayleigh scattering in the visible range is stronger on the violet end of the spectrum than the red so combine this with the spectrum of the sun and you have blue skys. The difference is the intensity of light comming from the atmosphere. On Mars it would be a dim blue sky.

"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."

Mie scattering deals with scattering by particles and not molecules. Because most of the particles are larger than the wavelengths of visible light, the red end of the spectrum is scattered more strongly than the violet end. The particle's actual color is only a part of it.

"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?"

Our planet also has liquid water based geology going on today. This tends to either keep the dust wet and matted and or helps it become sedimentary layers which don't tend to fly around much.

On Mars, due to the atmospheric dryness, all the aeolian transported rock particles (which I'll call sand, but it's much smaller than sand) remain free and mobile to fly around sand blasting other rocks, which incidently makes more "sand". Some particles are sooo small, a population of them remains suspended in the atmosphere.

Ron Greeley wrote an article describing why, in pictures from the duststorm during the recent invasion of Iraq, the sky was orange.

Red hematite pigmented sand and Mie scattering. On Mars, the dust isn't necessarily red, but there's a bunch of it.