#1. "RE: Purple cast on HDR Images" In response to Reply # 0
I think it has something to do with certain lenses in dark areas of the picture. I have a 14mm prime lens that does that to me once in awhile. I can take the same shot with the 17-35 at 17mm and not get the purple cast. If you can, try the same shot with a different aperture and make sure there is no dirt spots on the lens. Larry http://www.larryandersonphotography.com
#6. "RE: Purple cast on HDR Images" In response to Reply # 4
Oh, and another thing...
If you processed the raw NEFs with Photomatix, you might also try the following experiment. Bring the NEFs into a specific color space using a raw processor like NX2 or LR, export TIFFs and use those in Photomatix.
This adds a step, but my observation has been that Photomatix is less prone to adding artifacts when it's dealing with images that already have a tone-curve applied via an embedded color profile.
I personally prefer NX2, since I can apply Picture Control settings and use arbitrary color spaces with it; but if you have LR, then use ProPhotoRGB for a big space.