Strange colors in FCP X -- graphics problem

Final Cut 7 worked fine. When I upgraded to FCP X, I get strange colors in most of the clips: some colors turn to noisy purple, some are intense yellow, etc. and so on. It look just like "False Colors" on a Red camera.

These clips are from Red, Alexa, Sony XD cam and some are just plain Quicktimes (Output from Final Cut 7 or Compressor). Interestingly, anything shot in Log color space (and therefore low contrast, low saturation) shows no problem at all. Not all clips from any particular source have this problem, but most do.

I'm using a Mac Pro with two graphics cards: a Geforce GT120 runs the displays and a GTX285 is the GPU -- this is the setup necessary for Davinci Resolve and both are on the certified list for FCP X.

The problem only occurs in FCP X. In the timeline, the clips look normal, it is only in the viewer that the colors go crazy. FCP X runs fine on my Mac Book Pro; it is only the Mac Pro that has this problem.

The problem is bad enough to make FCP X unuseable. Any ideas?