Bob,
Just some quick info. On any powder paint colors you mix you will never get a true pigment. If you mix 2 tsps of blue and 2 tsps of yellow, you will get a shade of green. Not a solid green. In my experience you can get some interesting colors this way, but your color will never be true, it will be close though. (ie.... if for some reason even with measuring, you get too much yellow, and the blue packs down better than it did last time, you will be a shade off). All of this seems trivial, and probably doesn't matter, but just so you know. Anyway also, keep good detailed records of your ratios, that is very important for future duplication.

PS..................Your powder paint is going in the mail today.