Grey was a colour.
Earth in the 30th century had grey land and grey seas, with grey cities linked by grey highways across grey deserts. (TV: The Mutants)
The Inter Minorians, (TV: Carnival of Monsters) the Grey Man's race (PROSE: Falls the Shadow) and the Sittuun (PROSE: Night of the Humans) had grey skin.
When the Third Doctor encountered a new Dalek command structure, Dalek drones were identified by their gunmetal grey casings. (TV: Day of the Daleks, Frontier in Space, Planet of the Daleks, Destiny of the Daleks)
The Renegade Daleks had grey and black casings. (TV: Resurrection of the Daleks, Revelation of the Daleks, Remembrance of the Daleks)
The Eighth Doctor wore a battleship grey cravat after his regeneration. (TV: Doctor Who)
The Master wore gunmetal grey cargo trousers when on hiding. (TV: End of Time)
When she joined the Ninth Doctor, Rose Tyler wore a grey t-shirt. (TV: Rose, The End of the World, The Unquiet Death, Aliens in London; COMIC: The Lost Dimension, etc.)
Clara Oswald sometimes wore grey sweaters. (TV: The Magician's Apprentice|The Witch's Familiar, Face the Raven, Hell Bent)
Donna Noble wore an iron grey dress with her mauve cardigan. (TV: Silence in the Library|Forest of the Dead). She also wore a gunmetal grey sweater dress. (TV: Turn Left, The Stolen Earth|Journey's End)
Jenny Flint wore grey waistcoats with her white shirts and her cravats. (COMIC: The Lost Dimension)
The Book of Lies said that a great greyness was going to fall over the universe. It also called Rassilon the "Great Grey Eminence". Griffin's eyes were grey. (PROSE: Unnatural History)
Kenossium's eleventh incarnation had grey eyes. (PROSE: Lords and Masters)
According to one account, the Seventh Doctor had grey eyes. (PROSE: Timewyrm: Exodus)
The Kaled heart was grey. (TV: The Stolen Earth)