Well,
first of all, a brush painting job looks cheesy to say the least. I wouldn´t recommended at all, it will look like those "nice" kindergarten drawings some co workers proudly show on the walls of their office. I think spray painting is the only decent way to go, if you are working with several colors, prime the surface and then start with the lightest color, mask whatever you want in that color and after that, apply the second color.

As for the "clouding" effect you describe, it is probably caused by high air humidity. If you are using a spray gun or an airbrush, install a water trap in the hose.

Ricardo