I don't think a different coloration is acceptible. I'd say it was a flaw...and ask to exchange it...hopefully with NO shipping fees. That's a beautiful sofa! But.....the coloration would bother me daily. You could put a throw over that side of the couch...no one else would notice it...I'd notice. It's up to you....

Edited to say: If you apply saddle soap or a leather cleaner...it might darkern the section and "fix" the problem...

It's difficult to tell from one photo how significant the color variance is off. However, I can tell you that the leather is Finished (or painted), and what has happened if you see a color variaiton is they used a hide that was in inventory from a different dye lot to cover that segment. This is not unusual, a factory will often have leather pieces from three to four different dye lots. Let's say they had 300 sf of leather from batch A and need 330 to make your piece. Rather than order a new lot of typically 4,000 sf of hide, they used the 30 sf from a different dye lot B.. That's faily common in the trade. However, they should not put that small segment in a prime location, and that's on the Cutter. When you do that, the Cutter should put that piece from B on the lower outer arm, or in the back. Is it accepectable? Depends. Omni is not a high-end maker, so at their plant it may very well be. At a top-flight manufacturer like Hancock and Moore or Whitmore-Shreill, that would not have got past Final Inspection.

You cannot darken the hide, its a finished leather (painted). Your only recourse is to return the piece and request a new one.

Are all 3 pieces—the 2 sofas and the loveseat—the same color? You may have to deal with each piece being different hues, once you receive the new loveseat.