The 52-year-old star was spotted at the Get Reading festival in Trafalgar Square only two weeks ago with noticeably darker locks, which suggests that he has been dyeing his hair up until now.
The star recently revealed that he isn't worried about getting older.
In an interview, he said: "No one claps their hands at every birthday and thinks, 'Good, I'm 51 now.' But it doesn't keep me awake at night, I don't think.
"You care less about everything. Or you care less about silly things."