?
Google image source:
http://www.google.co.uk/search?q=cat+777d&tbm=isch
Or did I miss the joke about them being dusty?
Yes, they get dusty and then may look grey, but not like raw metal:
http://www.scpm-international-concas...-occasion.html
(I chose this one, because it shows part of the grille rather black and the other rather grey.)