My bad. I was editing the unedited original cause I liked the quality of the greens on that version much more than the next stage. Especially since you were trying to saturate them more. But uhh, good job! You already did half the things I suggested. XD
Also here's a tutorial by someone else that's much more organized and better than mine:
http://androidarts.com/art_tut.htmIt covers color, but also lighting and a couple other things. You can't really discuss color without lighting.
I'm going to break down how I see iLKke's piece is working.
Their colors are a little bit fantastical (made up essentially), but they still follow real world lighting principles. (as an aside, if it were a real object, it would have to be iridescent to get that kind of color out of it.)
The planatoid has a very warm light shining on it, and then shifts to cool colors. The band of more saturated green before fading into the shadows is because light does create a more saturated band around the edges of shadows. (blue could have been substituted instead, but I think they used green just to have more a more funky feel to their colors)
And then their shadows are warm, but they do get a little cooler as they terminate to the darkest value.
In the overall composition, the robot has just hints of color on him. Making him remain mostly grey makes him a focal point in contrast to the colored planatoid, which is still rather muted in saturation or it would draw too much attention to itself. Also the planatoid's brightest value is not as bright as the values used on the robots face, so it directs the eye rather nicely to what we should be seeing.
In general I see orange, green, and purple as the overall color scheme. Also with saturated vs unsaturated as a big part of the composition as well.
And as a further note, everybody kind of develops their own color preferences. I wouldn't have particularly chosen the colors that iLKke used, but it doesn't mean they don't work, since they follow the basic lighting principles.