Why do goalkeepers wear a different colour?
It's a rule, not just a fashion choice — the keeper must be told apart from teammates, opponents and officials, because they're the only outfield player allowed to use their hands.
The short answer: the Laws require it
A goalkeeper wears different colours because the Laws of the Game demand it. Each goalkeeper must wear colours that distinguish them from the other players, the referee and the assistant referees. It isn't about style — it's so that everyone on the pitch can instantly identify the one player with special privileges.
Why it matters: the hands
The goalkeeper is the only player allowed to handle the ball, and only inside their own penalty area. For that rule to be enforceable at a glance, officials and players need to know at all times who the keeper is. A distinct kit makes handball decisions, and the whole flow of the game around the box, simple to judge — imagine the confusion if the keeper looked identical to the ten outfielders.
A bit of history
Early football didn't always distinguish the keeper, but the English FA moved to require goalkeepers to wear a different-coloured shirt in the early 20th century, originally limiting them to a small set of colours. Over the decades keeper kits went from plain jerseys to the bright, sometimes garish designs of today — partly practical, partly a way for famous goalkeepers to stand out.
More than one clash to avoid
Because the keeper must differ from both teams, both referees, and be visible against the crowd, clubs carry several goalkeeper kits and pick one that clashes with everyone on a given day. That's why you'll see a keeper in lime green one week and orange or purple the next: it's not vanity, it's the practical business of making sure the one player who can catch the ball is never mistaken for anyone else.