I have two BEL AIR singles... and both in different colors (front cover, and inside). One is natural and one is bluish.
So... if the one with natural colors is "standard edition" then the blue one is what? Printer issue?
It was my first thought too. But inside it's bluish too.
Sorry for bad photo, my phone sucks ;-) (believe me it's not shadow od bad quality - colors are a little different for sure)
Besides front cover and bottom inside the rest is the same.
But maybe it's because of sun? Maybe single was standing opened on display - that's why front and bottom inside is different...?
BUT can full color cover fade to one color?
EDIT: I think you're right. Cover is in one piece (back & front) and there's no bluish colors on the back.