I have two boy kitties that are grey though, but if I got another grey boy kitty his name would be Frodo or perhaps Legolas and if was a girl, Arwen. Gotta stick with the Lord of the Rings names, since I already have the theme going..
If I didn't have my theme though I'd name a girl Shimmer and a boy Shine. (Both Gandalf and Samwise have really shinny coats and they shimmer and shine.)
My 1st cat when I was in my own place was a grey cat. My friend had a litter and I went to look at them and had the named picked out-MC (my cat) and called out the name MC and the first one that came was mine (for 14 yrs).