I was once in the same position, buying a light brown pair of AE's off the Bay. The vendor at least acknowledged a 'slight' variation in shade as a consequence of one of the pair being a display model. It was a good deal more than slight when I got them - very similar to yours. I really liked the shoes and decided to keep them and try what I could to get them more closely matched. Mistake. Nothing really worked. Best I could do was diminish the mismatch somewhat, but I could always tell and it always bothered me.
Send them back.