Are they "nude?"

If not, then the final (really the first) layer was gel coat that can be made to look any color... such boats which are typically white, or truck shells which can be almost anycolor. The gel coat has no structural strength, but is simply a color layer. In fact if I remember correctly the resin has no structural strength either... it is the fibers that do all the work, and the resin simply is the binding for the fibers.