I've currently have the above, Green sides and black back; and have also had the gray sides and blue back.
For the green one: I love the green, but wish it was more neon. In certain lighting it looks neon like I want, but other times it looks like an unripe banana which is offputting imo. I don't think the black rim on the front goes well with the white, and the back is barely transparent and looks like those gummy cola candies in bright light (not black, but ends up being a champagne brown color). When it is dark, and it looks black, I think it looks great. Overall, it is my daily case and sometimes I like it and sometimes I don't. I think it would look better on a black phone.
The blue: I loved everything about the blue back (it was much more transparent than the black) and it went well with the white iphone. However, I hated the gray sides and thought it made everything look cheap.
I'm hoping they will come out with more color combos, because everything else about this case is spectacular. It's about $17 on amazon now, and I think that is a good buy. I bought it at $27, which I think is too expensive.