Unfortunately, display issues manifested by vertical lines and color marks, uneven screen, uneven colors, gradient on grays, pink and yellow tints, as well as uneven brightness on the Galaxy Note 5 display are common flaws seen on AMOLED devices including the Galaxy S6, S6 Edge, S6 Active and the Note 5. Even some new owners of Samsung's latest Galaxy flagship smartphone, the Galaxy S7 have similar concern when using their new phone outdoors.
While the latest AMOLED technology has been enhanced, it's not that perfect yet. In other words, it too has some minor downsides like the ones we've tackled in this post.
In terms of vibrancy and vividness of the colors, super AMOLED devices like the Note 5 perform better than IPS LCD devices but their visibility in bright sunlight is another story. So far, no official update can rectify these minor display flaws. That being said, your only options include a screen replacement, phone replacement, and avoid using your device outdoors or subject your phone to direct sunlight. Other users have resorted to a temporary solution by configuring auto-brightness settings on their phone to whatever works best for them.