Yeah, I think it'd be easy not to be vain about hair color when one looks, sounds, and looks as good with gray hair as Clooney.
His father Nick Clooney (who was a local news anchor when I was growing up, and whom I got to meet once) always looked good with silver hair, and I'm struck by how much more George resembles his father as he gets older.
Anyone else without pre-existing fondness for the property think The Man From U.N.C.L.E. is kind of a lame name, though? I didn't grow up with the show, but I have a hard time picturing something with that title doing as well with the unwashed teen-demo masses as something shorter and punchier a la Get Smart.
On the other hand, it's been an inspiration for other titles continuing to the present day -- there are upcoming Marvel Comics-based TV shows called Agents of S.H.I.E.L.D.
in live action and Hulk and the Agents of S.M.A.S.H.
in animation. Stan Lee and Jack Kirby created S.H.I.E.L.D. in the comics just a year after TMFU premiered, and were drawing on it as an influence (as well as James Bond organizations like SPECTRE -- and keep in mind that Ian Fleming had a hand in the creation of TMFU).
The name U.N.C.L.E. was chosen because it evoked both the United Nations and Uncle Sam, but was ambiguous about the organization's actual affiliation.