Stock 914/6 was black... and some grain from the fiberglass was visible.
According to Pat Paternie in his Porsche 911 book, the color of the shroud on some early 911 motors signified something: the 911S engines had red shrouds, the E engines had green shrouds and the T engines had yellow or black shrouds.
My opinion: It's your car. Do what makes you happy.