I feel sceptical that Cat graders were ever grey??? But I have no idea really. Cat bought out Russell in 28 and didn't really come up with their own line until 30, so I thought??? The Russell company and lineup continued through 29 painted dark red.
I'm not sure when highway regulations dictated that all construction vehicles be either orange/bright red, or yellow. But I think it was between 30 and 32. Which means my reply has zero to no significance whatsoever as per your question ...
[img]http://img404.imageshack.us/img404/8752/funnyim0.gif[/img]
I knew the cats were grey in that time frame, but did not know about the graders.