Amir,
How can you be sure about the paint adhesion on a surface that comes out of the mold?
Basically all lay-ups including the painted in the mold ones has mold release residues unless otherwise the surface is cleaned with a solvent which does not effect the paint but cleans the mold release agents.

Therefore, a primer coat is not required but a fine sanding or scuffing procedure is advised before spraying colours on the surface.