Rainbow Spotted

Yep, I've seen it a few times in-game. Doesn't appear to have any impact on gameplay, but it's a cool visual feature.

I see those

They got implemented about the time Alolan forms came in the game. I‘ve seen them multiple times back then, but quite rarely last two or so months

Yea, I've seen it as well but as far as i'm concerned it doesn't really mean anything.

I think they pop up when rainy weather turns to cloudy or partly cloudy. Haven't really looked hard for a specific correlation with the weather, because it doesn't appear to change anything. That could change in the future.

I think at the end of each rainbow is an EX pass not on a Monday 1pm to 2:30 pm