I believe the difference in saturation and hue that I'm seeing between the IS settings has to do with how the auto-exposure is reading when the IS is on and when it is off. I have no idea why, but with the same shots, of the same subject, distance, framing and ISO settings (100), I got 640th sec at F7.1 with IS off and 500th sec at F/5.6 with it off. So I did it again, thinking maybe the light changed between shots (a matter of a few seconds). On the second test I got 500th at F/5.0 with IS off and 400th at F/5.0 with it on.
Now, while this proves the light was changing because of the different exposures between tests at the same IS setting, it does indicated that the readings were varying each time between IS on and IS off.
So I believe the saturation and hue are the same regardless the settings, but the degree of that saturation/hue varies according to the f-stop/shutter speed relationship, which for some reason that eludes me is changing between IS on and IS off. As a general rule, exposures toward the darker side are going to have more saturation (and more dramatic hues), while those on the brighter side have less.These exposure parameters can be controlled by underexposing by -1/3 or over exposing by +1/3 as needed, or by auto-bracketing shots and then picking the one with the perfect exposure/saturation/hue. (Exposure, of course, can also be altered in PP software to get the same thing, but my attitude is to get the best possible shot from the camera and do as little in PP as possible to maintain the integrity of the image, especially with JPEGs.)
As I mentioned above, I shot all the test images in RAW/JPEG, and saw no appreciable differences between RAW and JPEG images in my camera's computer software imaging program or on Infranview.

Generally speaking, I'm getting a slightly darker exposure with IS off than with IS on, and this is why those shots appear to have more saturation and a slightly richer texture, which I actually prefer for images I submit for publication.
The tests I just conducted re-confirm that general image sharpness is better with IS on than with it off and on my tripod. (This time, I might add, I set my camera on mirror-up, 2 sec delay for tripod shots to cut down on possible mirror slap and shake during exposure.) I will admit, however, that my tripod is a WalMart bargain and no were near professional quality.
That’s because I find a tripod impractical for the kind of wildlife photography I do and use a good monopod instead. Most of the time, however, I hand-hold my 200mm F/2.8 for shooting critters.
While my experiments have answered some questions about IS, and have given me some clues to getting the perfect exposure with it either on or off; and while it has renewed my faith in my K20Ds in-camera IS technology, this does raise the puzzling question of why the exposure meter is reading slightly differently between IS on and IS off?