Mmm... I know this post is old, but where does it say that Raijin is often portrayed as a red oni, and Fujin as a blue oni? I can't find sources for such affirmation anywhere.
Fuu: as in Fuujin, god of wind.
Often portrayed as a blue oni.Rai: as in Raijin/Raiden, god of thunder/lightning.
Often portrayed as a red oni.