I'm not sure but you may be going for the "patina" look. Street rodders who want guys to believe they have found the "barn-fresh" car of a lifetime are painting their hotrods this way. I saw a '32 Ford in "Streetrodder" mag. that had a modern fiberglass body but had primer showing thru the faded paint. Some guys are going to such great detail they drill pitting holes into their fiberglass. Another option is called "suede". Guys just keep their cars in primer. There are a number of different colors.
It's your ride so paint it to impress yourself. That's why we're spending all these bucks, ain't it?

Six volt guy living in a twelve volt world