Not sure if anyone picked up on this, but notice what they used for background compositing:
Had they used blue or green screen, then the reflected blue or green created by those screens would have thrown off the overall color tone/saturation on the actors/props. No matter how well they were matted into the background, the lighting on them would have been slightly off from what it would have been if they had actually existed in that environment.
This is the level of attention the VFX artists/supervisors pushed for with Dune and why that movie just looks so much more real than what you would find in a Marvel movie or any other big budget VFX movie. You can see that philosophy talked about in how they even shot the Ornithopter's using t wo helicopters to get real life camera distances, angles and dust effects. Other things to note when watching Dune: The star's faces are not always perfectly lit during a VFX sequence. They go into complete darkness when a VFX explosion goes off in the background because that is what would happen should an actual explosion been filmed. The camera would have dropped a few F-stops to get the exposure on the explosion correct while throwing the foreground actor into complete darkness. Normally, the mentality is "keep the big budget star visible at all times as that is what the audience is paying to see!!!" Err...not really.
Dave