His books are enjoyable, but they don't do much to challenge the reader's 'gray matter'. [='intelligence']
His hair is 'graying'. = He has 'graying' hair.
What will you do when you are old and 'gray'?
(..) Dialogue: ..,Default,,,of it last Friday. Dialogue: ..,Default,,,Booth. Dialogue: ..,Default,,,He painted the railing. Dialogue: ..,Default,,,It was gray in\Nthe satellite image. Dialogue: ..,Default,,,Take a look.\NAh, you, have a seat. Dialogue: ..,Default,,,Sit down. Dialogue: ..,Default,,,Sit. (..)2016 TvShow: Bones Title: The Death in the Defense Season: 11 Episode 11