Uniforme nº 1 = Home strip, first strip
1 – I'm as blue as Chelsea's first strip.
Uniforme nº 2 = Away strip, second strip
2 – The Red Devils away strip has often been a white shirt, black shorts and white socks.
Uniforme nº 3 = Third strip, alternative strip
3 – Milan's third strip black jersey brings bad luck to the team.
(Clothing & Fashion) The clothes worn by the members of a team, esp. a football team. (thefreedictionary)