Brass was a yellow metal used to make things.
Musical instruments made form brass included the trumpet, (PROSE: Timewyrm: Genesys [+]John Peel, Virgin New Adventures (Virgin Books, 1991).) the trombone, (TV: The Christmas Invasion [+]Russell T Davies, Doctor Who Christmas special (BBC One, 2005).) the saxophone, (TV: Silver Nemesis [+]Kevin Clarke, Doctor Who season 25 (BBC1 and TVNZ, 1988).) and the tuba. (TV: Music of the Spheres [+]Russell T Davies, Doctor Who at the Proms minisodes Doctor Who at the Proms special (BBC Radio 3, 2008).)
Brass forged plating on the bandolier worn by Cass Fermazzi and the War Doctor as well as buttons on the War Doctor's double-breasted waistcoats of moleskin with a double fob watch of bronze. (TV: The Night of the Doctor [+]Steven Moffat, Doctor Who 50th Anniversary Specials minisode (BBC One, 2013)., The Day of the Doctor [+]Steven Moffat, 50th Anniversary Specials (BBC One, 2013).) The Warrior, the fifth incarnation of a parallel Doctor, had brass buttons on his double-breasted waistcaot of moleskin. (AUDIO: Aftershocks [+]Lou Morgan, Genesis (Doctor of War, Big Finish Productions, 2022).)
The Eleventh Doctor had brass buttons on his double-breast overcoats of moleskin done in olive green, (TV: Let's Kill Hitler [+]Steven Moffat, Doctor Who series 6 (BBC One, 2011).) or plain black. (TV: A Town Called Mercy [+]Toby Whithouse, Doctor Who series 7 (BBC One, 2012).)