Hi Spikey!
I'll bet they're not the same! These things are printed all over the world (mostly price dependent now), and unless you have top notch quality control people, and are using state of the art precision devices for color—they will always vary a bit.
The general public wouldn't even notice a thing—but a Towie, who is looking for every fleck or color change that he/she can find, will spot it in a minute—as you have.
But you have piqued my curiosity, since this is my field, and now I'll be on the lookout in various stores to compare covers! BTW—how many copies of SS do you have, anyway? Storing up for Y3K?
Love, Catherine
"If we don't change the direction we are headed,
we will end up where we are going."
—Chinese Proverb