Ty,
I get paint mixed all the time at the local auto paint store. The only thing you have to be careful of is if you are using a pearl or metallic paint, you have to ask if it uses a liquid additive for the pearl (or metallic or whatever). If it's liquid, it's probably in a urethane carrier. I just have the guy substitute a dry form of pearl or metal flake or whatever. He will complain that if he does that it will not be EXACTLY the same color. I will say that fine. Then get home and mix in my own binder (dope). So far, no problems with this method, though I've had some unpleasant experiences that taught me this.