My test instance consists of three mods

When Aura is low, rain looks normal. As it gets higher it glows bright white as shown in the video. Removing Nature's Aura resolves this issue.
https://streamable.com/fr6y1b

Hmm, I can't reproduce this on any of the graphics settings, not even Fabulous :(

Yeah, not sure what the cause was but I've just reproduced my tests with the latest versions of everything and it seems to have been fixed somewhere along the way :D Gremlins.