USA Pheasant Color Shift. Error?

I found this digging in my collection. The stamp on the left is what its suppose to look like, the one on the right has a black color shift (black has shifted slightly to the left). Is this a major error, and if so, is it common.

I would not consider this an error. Simply a poorly registered stamp. The color misregistration, while not common, is not significant enough to warrant any premium. Usually, color misregistrations need to be several millimeters off (or produce an interesting and distinct change in the design), to warrant a premium. There tends to be a fine line between a poorly printed stamp and a printing freak with an increased retail value.

There is a variety of this stamp, #2283b, where the red has been removed from the sky. It's very apparent when the two stamps are juxtaposed.