I sure wish I could help you, but I am still on my first Fallout 2 play through.
Is this one of those questions where you go insane if you don't have the answer? I hate those. I saw a movie once that had jim carrey in it and I could not for my life figure out who he was, for like a week...
Anyways good luck, I'll look into this.
Edit: From the wiki itself:
"As for looks in New Vegas, it is identical to its previous appearance in Fallout 2, except it has a grimier look and the goggles seem to be cracked."
I interpret this as so: it is gray due to it to appear to be a grimmer look. Meaning old or weathered and possible it was white before.