I would have to think rainbow stories/prophecies and legends and ceremonial practices should have probably been a world wide practice of differing types at one time or another.
Since the rainbow is known by all peoples.
I would imagine kinda big like rain,thunders,water,sun.
Australian aboriginals have a rainbow serpent.
As far as all peoples coming together in a good way, it would be nice, and we do practice things in many ways, to make that happen, but no rainbow knowledge involved.
Just because I believe it today, doesn't mean I will believe it tomorrow.