Bobby Moncur skippered both sides but revealed he committed the cardinal sin when he joined the Black Cats from Newcastle in 1974.
The ex-Scotland defender, now 67, switched clubs just a few weeks after captaining Newcastle in the FA Cup final against Liverpool.
Moncur's reward for reaching Wembley was a sponsored car - emblazoned with his name, the Magpie mascot and painted in Newcastle colours.
"I carried on driving the car, forgetting it was done up in black and white," he said.
"I remember driving to Roker Park with all these hostile faces looking at me.
"It was only when I got out that I realised.
"I went back to the garage and they gave me a brand new red one."