My first Paperwhite had distinct bright pinkish and bluish-greenish blobls in various places on the screen, so I contacted Amazon Kindle support via online chat. After I described how the screen looks like, they send me a replacement.
The replacement device that I received this Monday does not have any multicolor spots. It just has a noticeable brighter right bottom corner, without color hue change, only white intensity. That's probably not a problem with the screen, but that the right-most light gives little bit more intense light comparing to the other three.
On the light level 18, it looks like the most of the screen surface is made of a lower quality newspaper-style paper - not bright white, but dirtier-grayish, and lower right corner, may be 4-5cm. in size, is made of higher quality brighter white paper.
I have not yet decided if this bothers me enough to contact Kindle support again.