Broken pixel

You had 14 days from the date of purchase to return this iPhone for either a replacement or full refund. After that, the Apple Hardware Warranty is the valid instrument. That warranty basically covers manufacturing defects. The following is an except from the warranty document:

Apple Inc. of One Apple Park Way, Cupertino, California 95014, U.S.A. (“Apple”) warrants the Apple-branded hardware product and Apple-branded accessories contained in the original packaging (“Apple Product”) against defects in materials and workmanship when used normally in accordance with Apple's published guidelines for a period of ONE (1) YEAR from the date of original retail purchase by the end-user purchaser ("Warranty Period").

Ref: Apple One (1) Year Limited Warranty - Apple

Again, if an Apple technician confirms that it is a manufacturing defect, you may be offered a replacement phone. Every Apple-product purchaser is under the same warranty. However, some countries may offer additional protections that you may want to investigate further.

At this point, you need to make a Genius Bar appointment at your local Apple Store or Apple Authorized Service Provider to have them take a look and provide you with your options. If they determine that it is a manufacturing defect, you may be offered a replacement at little or no cost to you.