Was trying to put some color on my Barrow's heads and was having a little trouble. 
I was pointed toward a powder interference "stuff" to mix with paint.  Kinda neat because you can mix it into any color and get traces of the interference color in anything. 
When I did my swap bird I tried to come up with a method that achieved results I was happy with.  While I found a happy resolve, I was concerned that duplicating it on the 2 I still needed to paint would be hard to do.  Well last night I was messing around with it and it just wasn't going well.  Was getting thick clumpy looking paint, rather then a nice smooth finish.   Not really sure what made me do it, but I dabbled my brush into a little paint thinner and wiped it over the top of the already painted head.  Suddenly all the "thick" stuff smoothed out and the interference color just seemed to blend in.  Surprised by how easy it was, I proceeded to do the second head with similar results.  Today I'm looking at the dried heads and see the color and look I wanted without any real brush marks in the paint.
After the fact I thought about the fact that a lot of painters thin their paints, I just never seem to.  So for those new to painting (like myself) when the paint just isn't going on like you hoped, try adding just a touch of thinner.
SInce these were all gunners I'm just using an oil based Rustoleum Flat Enamel in black and white.  The powders I have are blue and purple and I mix a small amount of each together before applying to the head.
I don't have pictures tonight as I write this, but I'll post up some in the near future.


~Dave

Bruce,

Somewhat the same thing.  I think the interference paints and powders are a little more subtle and require mixing with something wet.  The 2 I mix are blue and violet but start with a gray appearance until they mix with paint.