Steve, the Javelin team also used a zolatone style of paint on their interiors like some of the Mustangs did. I think the light gray was chosen for the chassis and engine compartment on the Penske cars to make any oil leaks or chassis cracks more easily recognizable. A lighter color in the interior would yield a cooler interior temp, which would be helpful during the long races. Yes, it required more work to mask everything off but people liked to follow Penske's lead, Success breeds imitation.
