well, even my 503 with decoloration, is considered a good unit.
I don't think it's worth returning for; going through all the trouble, missing out on the fun for 2 weeks...
Besides, even if there is decoloration, or hue change, you won't notice once your mind sets on reading the book.
It's very gradual. And if you're reading the book and still notice, means you're not really into the book, or are just reading too slow.
Pushing your reading to 3-4x speed of regular reading (also called speed reading) should get your mind off the colors
