i dont think it should be hard at all..if your spraying it your self just add some pearl to the paint..
they also offer a gloss in all those colors..
but what i would do is mix it, and then get a satin or almost flat clear, and clear over the flat to give it that satiny look...
but i think it would look sick in one of those flat colors..there allmost satin as it is..

also check out towards the bottom of the page..the metallic flats are sick..