From what I can tell, you can get that sky to change its color by manipulating the render settings. You can have it generated by the background color in sketchup or the sun and sky settings in sketchup.
I've played around with Maxwell a tiny bit and it does have a lot more control, but that also adds to the learning curve. I couldn't produce an image as effortlessly as the ones above in Maxwell - although with time and learning its interface I'm sure that I would have no problem. Maxwell is incredibly fast though, which is nice.
I'll just say one short thing about Revit and ArchiCAD - I don't want to create one of those flaming threads that are 29 pages long but every post basically says the same thing: my program is better than yours. They both have their issues - neither is perfect by far. I have done cost estimating in both (neither is automatic and requires a bit of set up to get done) and I have produced CDs in both. I find it easier to make objects in Revit with the family editor but maybe thats because I'm a visual person. I've attached a family that I made yesterday in about 2 hours and I really have limited experience with families. If you have Revit or a demo, you can check it out.
Both are very capable programs. The #1 asset, IMHO, for either program are their respective community forums. Without these forums I think people would be a lot less likely to stick through the troubling learning curves.
If I had to use ArchiCAD again I wouldn't be too upset - just don't make me go back to flat cad.
RA 2012 x64, Piranesi 6 Pro, Sketchup 8, Windows 7 Pro x64, Intel Core i7, 10GB RAM, ATI Radeon Mobile 5870