My iPhone 6 screen have dead pixels blackish on the top left corner and greenish color around the edges of the screen, never dropped, never got wet and never opened the iPhone, what could be the problem?

Hi

Your iPhone may require service. Before contacting Apple, Apple advises following these steps (check after each):

Restart your iPhone (force restarting it only if it cannot be restarted normally):

• Restart your iPhone, iPad, or iPod touch - Apple Support

Restore your iPhone to factory settings, being sure to make a backup first:

• Restore your iPhone, iPad, or iPod to factory settings - Apple Support

If the issue then persists, contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider to arrange for your iPhone to be inspected and to establish your available service options:

iPhone Service Answer Center - Apple Support

First you should backup your phone. It may be an early symptom of a known "Touch IC Disease". If that is the case the reason would be a mechanical stress (iPhone 6 is large) when carrying it in the tight pocket (the root cause is that this iPhone does not have underfill under certain integrated circuits on logic board making it more susceptible to physical damage - dropping the phone is not a requirement to trigger it though it may suffice). In general it is good to use a hardened cover for iPhone 6 family.

This is a well-known problem recognized by Apple (they even charge less than usual for that, at least in US, I do no know about different countries):

Multi-Touch Repair Program for iPhone 6 Plus - Apple Support

Are you sure you have iPhone 6 not for example 6S plus? The same issue occurs from time to time on a regular iPhone 6, but AFAIK there is no a repair program for regular 6.

how do you fix a stuck pixel?

more

https://www.google.dk/search?q=iphone+stuck+pixel&ie=&oe=