If I'm reading your question correctly, you just bought a new iPhone 14 Pro and there's a defect in the color on the back glass, is that right?
At this point you have three options.
- Return the phone for a replacement. Given that this is the latest model and should still be under warranty, you should be able to get it replaced.
- Replace the back glass. This is an extremely difficult repair, as the adhesive used on the rear glass of most iPhones is extremely strong, so it requires a heat gun or laser to loosen the glue enough to be able to chip the glass out of the frame.
- Replace the entire rear chassis. This saves you the difficulty of removing the rear glass, but that gets made up for by the fact that you have to transfer every single component inside the phone to the new housing.
Unfortunately, your phone is so new that no guides are available for replacing the rear glass or the chassis; you may be able to find YouTube videos, but none of the regular repair sites I'm aware of has any information on the 14 Pro.
I'd strongly suggest contacting either the seller or Apple itself to see about a warranty replacement.