So what is the difference between the white spine and black spine games?

I now its not related to date of release or publishers.

I have Shadowman and Loony Tunes Space Race, both were ports from previous generation systems and one has white and one has black spine?

Sonic Adventure 1 has white, 2 has black?

I thought at first maybe it was related to year of release, like 1999 titles where white and later were black, but MvC2 is a late 2000 release and is white...

I don't think its related to how the cover art would look in contrast...