Today at the end of the americas cd, both my boys had the rainbow appear in their game and i did not. They both caught 5 shiny larvitars, and i caught 2. The weather was partly cloudy most of event, rained in game… But showed cloudy(no rain but almost did). As event ended turned back to partly cloudy. Then they saw the rainbow on thier game. It was a good event over all, did need a focus on just the cd pokemon.
I hadn’t even thought about it until now but I had freakishly, and I mean freakishly good luck on CD, including non event species, and now that you mention it I did see a rainbow in game for the first time right before they started appearing, so that could be an explanation for it, although I would have thought others might have noticed that kind of correlation by now if it were true. It struck me as odd that I could only see it very briefly though, I wanted to take a picture with it but it already disappeared before I could react.