Like Troll said, a gloss black primer is best if you want a high-shine polished metallic affect. If you want a duller appearance, go with a lighter gray or white color, preferably flat. Unfortunately, every brand of metallizer out there has different requirements for best effect, some being the complete opposite of others.
There's a good summary article on different metallizers found at
aircraftresourcecenter.com. Just go to the 'Tools 'n Tips' and look for 'Bare Metal Finishes'. There are several good articles, including one on my favorite line, Alclad, though it's old enough to not have several newer shades like my favorite 'Airframe Aluminum' which I used on my Tojo in the other post.
One universal rule you can treat as gospel is to prep the plastic : get rid of ALL scratches and seam lines you don't want seen, and polish/buff it (NOT with a polishing compound), because ALL metallizers are going to show those blemishes better than if you drew a red circle around them with a sign saying, "Here's one!!"
As for your Red-Brown Baron, prime it with white primer like Mr. Surfacer, not regular white paint. Like Troll says, it sucks for coverage. That will make all the difference in the world for Red, Yellow and Orange colors. The general rule is they suck for coverage and opaqueness and the white helps to maintain the true color. Hope this helps.