An Odd question about insert background color

[jwb474]

I have been listening to the January releases and organizing the discs.
I noticed that the vast majority of the insets are black background followed by white back ground. Even both black and while for the same artist.
Also I have 2 Yellow, 1 Gray, and 1 Red background colors.
My big question is: What criterion determines the discs insert background color. Inquiring minds want to know

 

[Q-Eight]

I've noticed this, too. I had originally thought it was a way to differentiate between Pop/Rock/Soul titles and Easy Listening/Country titles.... and while it does seem that the all the country titles so far have black spines, Billy Paul and a few other non-country titles have black backgrounds. I then thought it had something to do with cost, as in black paper costs more than white paper and white ink is probably more expensive than black ink..... but then Helen Reddy, one of the newest titles has a black spin.

I don't know.