Roy G. Biv Day is an event in Moshi Monsters which happens once every year in April, typically around April 10th.
Roy G. Biv comes to Monstro City to make sure that there are rainbows all year round, even though there isn't any rain.
The holiday was created by Jenny.
The Roy G Biv Day wallpaper.
A Poppet looking at Roy on Roy G. Biv Day