Lot of improvements, some subjective regressions. Calling them dull is a bit...cheap.
If you wanted answer that they got degraded for reason x, then no, it hasn't happened.
Also few of those screenshots are actually concept shots from early development.
As usual with development, things change and move around, especially with frame rate requirements, new additional things to see in game, and so on and so forth.
edit: if I have to compare....planets don't tank my frame rate, not game become jerky when closing to planets, especially those who are landable. That had always taken me out of the game, and I am frankly very happy it's gone. I would like to see more colours, yes, but that's not essentially a deal breaker for me. Earth like planets look breath taking comparing to first painfully obvious 2D balls at launch. Rings are way less jerky, and still look good (I wouldn't mind for them to look better though). Stars imho have been gradually improved, and 2.4 update with better smoke shaders have done wonders to them. Stations - again, does not tank my fps flying into them, and we have big variation of them now. Outposts have gotten several nice updates in last two releases, I have seen retouches and improvements there too.
so scratch it, graphics have gotten better.