I believe Richard Todd the actor playong Guy Gibson came up with the actors would wear brown shoes to identify them. Being a black and white film there was no obvious difference. Richard Todd had a distingushed war career in which he was part of the parachute drop to support the taking of Pegasus bridge.
I've heard the same tale, with the addition that Todd - who still held a Reserve Commission - wore black shoes!
The problem was potentially greater with (actor) airmen - the SWO was in danger of a heart attack seeing all the hatless luvvies wandering around his Station, not knowing who was which.