As well as being yellow-carded or red-carded, you can also be shown a green card in hockey.
Cards are shown for rough or dangerous play, misconduct or intentional offences.
The umpire will issue an official warning to a player by showing the green card.
Prior to that, the player would probably have been given a verbal caution.
A yellow card means you will be off the pitch for five minutes or more.
A red card is given for more serious offences and sees the player leave the match for good.