I bought an iPhone 6 64GB in Space Gray from 5th avenue NY 14 days ago. I can see a grayish area at the top right corner, near to the charge display. It's hard notice in full brightness, but noticeable in low brightness which annoys me a lot. I know it will be tough to make apple genius understand but still can't live with it. I want to replace my phone. Will this one be covered by warranty policy? I have a slight hairlike scratch on the display.
The iPhone warranty in the US doesn't cover physical damage or cosmetic issues. The scratch will likely be judged that way unless it interferes with a function like multi touch.
Similarly, the return policy / window might be your best bet - especially if the LCD quality is clearly different than the rest of the display phones. Just because a light scratch happened - if there's a problem with the overall display, I would assume you'd be able to request an exchange / repair / warranty service to address the backlight and not the scratch.
If Apple's repair option fixes the scratch too, so be it - that's their issue and not yours IMO.
Lastly, get in sooner rather than later. Also, if you didn't buy the phone outright - be sure your carrier is OK issuing a second subsidy before returning the phone.
Sorry this isn't simple - but you've got multiple aspects to a repair/return to consider.