Club's "traditional" away kit colour's

[eyalluvitt]

The one day wonder all yellow kit at Highbury served us right for messing with tradition

 

[Alfie Budd]

Third, I think. Maybe something to do with neutral venues and teams having to wear contrasting colours for audiences watching in black and white.

It was 100% for TV.
Neither team wore their home kit for that 1968 final - Benfica wore white rather than red. It happened quite frequently in the black and white era.