I was going to use purple for my Cryx, but had already painted my Cygnar purple.
So I went with green, which was OK, but have slowly started using more and more grey.
Here is an earlier pic from my "green" period.
And here is one from my new "gray" period.
And something that incorporates both as a tweener.
Hopefully that gives you some ideas.
Also check around the internets. There are painting albums and old threads here on Dakka. And the
PP forums have a painting forum as well as the Cryx forum for more ideas.
And then what I do is if I find something I like I ask the person how they got a certain effect or scheme. I'd say my painting skills are good, but I am nowhere near a golden demon or studio paintjob. But trying new things is how you get better.