I have noticed that my Sigma cameras have the ability to differentiate subtle changes in in color better than my Bayer cameras. I notice it mostly in greens. My SD15 also seems to be a bit more color accurate than my Pentax and Sony cameras.
This is difficult to understand since it is known that the color separation of the foveon chip is not as efficient as the Bayer color filter. Most all reviews of Sigma cameras also talk about the great colors, IQ, and saturation at low ISO.
My only guess is that the broad spectrum sensitivity of each layer helps differentiate color at the expense of color noise at lower exposure levels. This could be achieved with the Bayer filters also but then the noise would be similar to the the Foveon. Overall public acceptance of higher speed must be more important than outright IQ.
Your experience is opposite to mine but on the SD9 whose color inaccuracy is documented ad nauseam in this forum. I sold mine in despair at those brown reds under artificial lighting which are still evident in the SD1 review on this site. Later, I bought an SD10 which seemed greatly improved in that regard. Meanwhile, my humble Nikon D50 produces very accurate colors in RAW/ACR (camera neutral profile). According to the MacBeth card, anyway.
According to a paper by the Foveon guys, the sensor does not suffer from "color noise" (actually color aliasing).
Public definitely seems to prefer huge resolution, enormous ISOs, ultra-high frame rates and now HD movies with stereo recording and not forgetting Wi-Fi, Bluetooth, Android with live touchscreens. All that for just a buck or two. Excuse me, while I puke