Well here's a very quick, extremely exaggerated example. I made it exaggerated so you can see the steps.
First block in your color.
Next use a darker version of that color to set in some details.
Next use a lighter version to add some highlights.
Then start to define things.
Smooth that out some.
In this last step I really defined things. I added tons of other colors, and showed what it would be like if other things were glowing or reflecting colors onto where I had the purple highlights.
All of this is done with a hard 1-2 pixel brush. Don't follow the steps exactly, do them how you feel neccesary. And remember that it won't be good the first time. These things require practice.