Quite easily - Warrington have alot of blue and yellow on their home shirt. Leeds have a predominantly blue home shirt, and a predominantly yellow away shirt, so they both clash with Warrington's home shirt. But to say that Leeds' home and away kits clash with each other would be ludicrous.
Say for example Leeds decide to have a predominantly red away kit one year, but then for that season Wakefield's home kit is red and blue. Leeds' blue home kit and red away kit would both clash with Wakefield's home shirt. Sometimes it just happens that way. The sensible thing would've been to have Warrington wear red and green or force Leeds to use a different colour for the final. But you can hardly blame Leeds when they were designing their kits at the start of the year for not accounting for what Warrington may or may not wear.