Simply put it's poor color management. Having worked in the print industry for far to long it's not the first time I have seen this, nor will it be the last. The good news is that it's an easy fix, but might be to late for some, but I am sure CPR will fix this for new ones. Also, hats off to CPR for the level of detail they put into this BG. Other then the bad color management it's a very faithful repro. And yes I am Canadian and spell color without a U intentionally.

When you are printing with a different process on different substrates some color shift even under the most strict color management should be expected, minimal when done correctly, but expected. What this Centaur suffers from is a clear lack of correct monitor color calibration/gamma setup OR soft proofing control OR conversion, OR some combo of all three. With centaur you have the input of the original art against a recreation of other art. Also, you can see the detail level on the repro isn't in the same ball-park as the original, but something you wouldn't see at 6ft. Color management is easy when you know what you are doing, but you can't wing it or this happens.