Yeah, I wonder if it's just the way the light catches it, because the surface is actually not smooth but rather bumpy/dimpled.
I just took a look at mine more closely and rotated it around a florescent tube and the color at those edges do change as I rotate the watch. Looks fine to me.
That said, if you really feel there is an issue, go to your local Apple Store (assuming you have one) and see if you can get an exchange. For something this expensive, if you truly believe there is something wrong with it, don't settle. On the other hand, be ready to be told that there is no issue if indeed you're just seeing changes in colour due to the reflection of the surface.
Couple of years ago, I had another indulgent purchase (iPad Pro with Magic Keyboard). When the keyboard arrived, I noticed it did not close flush with the iPad Pro. Somehow, the keyboard was just a little bit "tweaked". It was barely noticeable. But I quickly came to the conclusion that because this purchase is so expensive, I deserve to have a "perfect" model. I requested a refund and the online store employee was very understanding about it.