Why was red yellow cards introduced in football?

Answer 1

Originally, a player needed only to be notified that he was cautioned or sent off in order for that sanction to be applied. In the era of international play, language barriers sometimes prevented this notification from being properly administered. Referee Ken Aston introduced the concept of showing yellow and red cards to indicate cautions and sendings-off, respectively, in 1966 in order to traverse language barriers.