Hey,
I am also having issues with this, depending on the lighting of the scene its more or less obvious. I can totally understand what Matt means with the approximation of the clouds, but I dont really understand why this influences colors in the atmosphere as well.
Also, I am in general not sure why an approximation for accuracy on rendered clouds would introduce color shifts like that. From what I can see on your images Mr_Lamppost, its the same color shifts you have as I do. So everything thats blue-ish in the final render just looks a lot more orange in the preview.
We did some comparisons and corrections in Nuke with both images and there is definitely something going on with the colors. Also, I colorpicked the clouds at the same spot in preview and render (after applying an average blur to the same areas)
Preview value: 232, 230, 225 - Final Render value: 213, 215, 219. This is only a small difference at that point where I measured, but it spreads over the whole image and makes quite a significant difference in the whole images impression.
Here are some comparison shots:
From Terragen
[attach=1]
Comparison comped in Nuke, left is final render, right is preview
[attach=2]
So yeah, I really only care about color consistency and not image quality for preview vs. render. We want to make skies for HDR realtime rendering and would anticipate accurate results to have less guess work and trial and error involved.
Hope this gives some more insights
Thanks a lot!