I didn't see a photograph of Grant with gray hair until shortly after he retired in 1966, and he was completely gray. Though I think they did let some show in Father Goose
. He was the same age as my dad, who was gray with a Patrick Stewart hairstyle.
Found a good quote from Grant regarding actors: "I'm opposed to actors taking sides in public and spouting spontaneously about love, religion or politics. We aren't experts on these subjects. Personally I'm a mass of inconsistencies when it comes to politics. My opinions are constantly changing. That's why I don't ever take a public stand on issues."