I might have be misunderstanding what your looking for, or the look your trying to acheive but a pewter or any other grey/silver color might not necessarly work well with all the other silver/shiney you will have under there.

Just my opinion, but too much of the same color tends to "blur" everything. Using contrasting colors, such as the yellow block with the billet accessories will help the detail stand out better. Silver/natural on the tranny would likely work well because it would contrast with a different colored block and the underside of the car.

Just my opinion