I posted on this before, but the thread seems to have vanished. My problem was with a large interior, where all the distant walls had a strong blue cast even though there was nothing blue in the atmosphere model.

I finally found the problem after much experimentation, but I should have guessed it. It was nothing to do with the atmosphere, it was the model geometry. I discovered that moving the camera around caused the blueness to flip on and off. If the camera was within a certain volume, the blueness would be present, but outside that the atmosphere would render correctly. I should have guessed because I've seen that effect before if the camera is within a Vue boolean subtraction volume, but I didn't expect it with an imported Poser model.