It's the case when jerseys have different sponsors. Like in 2011-12 when the home jersey had one thing (Betclick) and the pink one another (Bolocco).
That's just common sense, but this was a more recent thing (last 3 seasons). Unfortunately I can't find anything to back up my theory, doing a quick check.
I remember that PL clubs in the past could only use their away kit in a certain amount of games, but that has changed now. The addition of third kits removes any possibility of a kit clash.
I remember going to a Coventry game against Chelsea back in the 90s and Chelsea only brought their home blue kit, so it clashed with the home team. The ref wouldn't let them wear it so the only option was to wear Coventry's away shirt, and they put a bit of masking tape across the badge. Coventry won 3-1 and I remember Frank Leboeuf throwing the shirt away in disgust at the final whistle
LOL