That's kind of strange because it occurs in episodes first on Arrow, then Flash and finally Supergirl.
Means we can watch starting on Colors and ending on cafe but they will not promote each other's channel which means most of people will miss the Crossover. Also, from next year Batwoman will arrive, and i guess that too will air on colors. They should get rights of next seasons of Supergirl after that they can promote crossover events. Because currently there is nothing like chronology in Arrowverse in India because of different channels being rightholders.