GW's initial advertising of Contrast was bogus, to put it diplomatically...
Contrast paints work best when thinned, at least 50/50 (sometimes as much as 4:1 in my experience) with Contrast medium and put down in several layers, instead of one big globbed on layer. It seems to help them settle more evenly and avoid some of the coffee staining effect. You also need to paint them on like a glaze, going in one direction only, ending where you want most of the color, in my experience. Especially for flat areas like on coats...
Using a large brush, like a Citadel M shade or Army Paint Monster brush, also helps on large areas, but that goes without saying I guess.
Make sure whatever you're putting it over is as smooth as possible. I've had bad results, because I've put it over brushed on paint, where I've used small brushes and had brush marks and unevenness in the layer.
A gloss coat over the top can help.
Also make sure you've got another brush handy to wick up any excess. But if you've thinned it enough, and you don't overload your brush, you shouldn't need to wick up much, if any, excess.
I've been using a few Contrast paints quite a bit, as you've all seen, and frankly at times I'm amazed at the results. I can't do skin to save my life, but Guilliman Flesh, thinned and applied in several layers, to the desired "tan" level, is a godsend...
They're very much a tool worth investing in, for getting things done quick and actually to a good looking standard in the right circumstances.
