Here's an idea with several colour palettes. Went for the isometric design in the title.
Figured I'd bounce off a few ideas and go from there to see what you're looking for.
Woooaahhhhh! That looks awesome!
I really like the first one (top-left blue), because it has the most '3dness'. The right and bottom designs look a bit too 2d/bright, and I think the black(ish) outline looks really nice. The middle left one looks pretty nice too actually.