You may have noticed that in certain areas where dark color gradients may be present, like near the terminator of planets, sometimes color banding is noticeable. Well, no more. One more benefit of the upgraded rendering engine is that such problems can now be very easily mitigated. It's just one line of shader code that adds an imperceptible amount of noise, just about enough to destroy the banding without otherwise affecting the image quality.
Example without dithering (up to revision 08c0079) - gamma in both images has been exaggerated for demonstration purposes, note the color banding in the center
Ah, yes, this one. Well, we know that it is caused by the cloud layer on the default atmospheres. It will be gone if you disable clouds by setting their alpha to 0 globally.
Unfortunately, I have zero idea what exactly is causing it. I feel pretty certain that it must be a silly one line fix somewhere, but have never been able to track it down and it bothers me quite a bit. Hopefully we'll figure it out one of these days.