Worldwide Athletico Madrid is more popular team then Athletic Bilbao, but do you know that the famous rival of Real Madrid was actually an youth affiliate team of the great in the past team from Bilbao. That's why both teams has similar kits. The only difference is that Madrid team kept the blue, inherited from Blackburn. ( More : https://steemit.com/football/@meanmachine/athletic-bilbao-club-colours). In 1921 Athletico became an independent club.