Ellian makes a good point: when trying to portray different colorschemes (with such a limited and low-sat palette) it's important not to mix in colors of distant/opposite hues, as they will neutralize the result. That is, try to keep a green thing clear of bluish colors and a blue counterpart clear of anything greenish (as yellow f.ex).

Again your outlines are becoming too thick due to the dark choices for internal-AA/shading. Directional light on the ring could also liven things up a bit.

In x1, it's kinda hard to differenciate colors, especially between the green and the blue... 
Anyway, excellent work, as usual.