The five new clans are combinations of three colours, however they specified that each had a main colour. They also changed the order of the colours on the cards.
My theory is that since the block is going to be about time travel and change, that once Sarkhan and Sorin have changed the past they will return to the present day where the clans will have the same colours, but their main colour has changed, eg. Abzan’s main colour changes from white-green-black to black-green-white.
The narrative theme of Abzan is endurance, but make the main colour black instead of white, and then you have a clan that will try and outlast their opponents at any cost.
This would mean the clans could change, but still be able to be used with their previous support.