I also don't really see a problem either. I do see the difference in lighting on either side, so the dark center area may be creating an optical illusion. It tends to be harder to notice subtle issues in a picture. Plus the spacebar is a very long key so it is more likely to twist/deform or to reveal an imperfection compared to all the smaller keys.
If you are concerned, then see what Apple or an Apple Authorized Service Provider has to say after they examine the laptop. More than likely they won't do anything if it is just a cosmetic issue or subtle imperfection which does not impact the use of the laptop.
Just to caution you since this appears to just be a cosmetic, personal preference issue....if it would be repaired....the repair may introduce some other new issue which may not be detected for a while, just something to consider. I just had to repair a laptop which had recently been repaired by an official Apple mail-in repair depot center....the repair tech had introduced several issues to the laptop which I had to address (stripped screws and several loose cables...one of which affected the lid sleep sensor)....the laptop was less than a year old and only had the single official Apple repair until I looked at it. I was shocked at what I found...not the first time to see such issues either although most times they do a good job. Personally I would recommend ignoring it, but I also understand this can be difficult for some people so don't be afraid to have Apple examine the laptop to see what they think.