DO I need to prime Plastic Trim before painting/ clearcoating if it is unpainted?

It usually comes primed.

So I guess that means if it's not primed, prime it! Thanks!

I use a medium gray. Any other color may adversely affect your basecoat.

Re: DO I need to prime Plastic Trim before painting/ clearcoating if it is unpainted?
 

Depending on the type of plastic it will need to be surface treated (plasma or flame) for the primer and paint to adhere correctly, especially critical on front bumper fascias and the like. It reduces the surface tension and allows proper bonding, you are better off buying something that is already primed.