Let me offer you a warm welcome to the Forum!
I'm sorry to hear that you experience with this camera was a lot worse than you had hoped for. I have been researching this camera myself because I am intrigued by this new technology of the Foveon sensor.
Your bad experiences are alarming, since color rendition is supposed to be this camera's strong suit. Some reviews have claimed that the auto white balance wasn't ideal under certain circumstances, but there is nothing to suggest that the camera performs this bad.
Another known issue has been with the early versions of the firmware, which is now at version 1.07.
One of the best layouts of the Foveon's strenghts and weaknesses by far - in my opinion - is this article by Mike Chaney: http://www.ddisoftware.com/sd14-5d/
which I would warmly recommend everyone to read, if they are interested in both the Bayer interpolation shortcomings and the new Foveon.
In some tests, this camera can outperform the vaunted Canon 5D it seems.
Overall, it seems that the SD14 can perform expertly, if the firmware is updated.
I hope you can find some possible root causes that can perhaps explain what you have experienced, but based on the severity you describe, I lean more towards the idea that something was defective in your issue.
Based on the results I have seen the Foveon produce, I'm almost certain that I will get the next Sigma DSLR with this sensor.
Do you have any samples you can post - both good and bad - I would very much like to see some if you have them?