@Cinisajoy: It has absolutely nothing to do with firmware version OR serial numbers. You a tiny step (as in "try factory reset, see if it fixes your problem") from turning into one of those clueless Kindle support people. @Monny stated that he/she bought 2 PW3s at the same time so there is 99.9% chances those are the same model/ same generation = no point asking for serial numbers.
@Monny: It's a well known fact that
every Paperwhite generation (to be even more precise every Kindle model with built-in light; so Paperwhites, Voyage & Oasis) has had the same problem with light "temperature" being in all possible variants between "sepia-like" to "significant blue tint" range. No 2 Kindle specimen in one model/generation are the same. If you had bought 5 PW3 you would probably have at least 4 different light temperatures
But, for example, on average PW2s had warmer light that PW1s there were still PW2 that had bluer/colder light that some PW1.
From Amazon's perspective their are all "correct". And what is better is subjective. I personally prefer Kindles with slight yellow tint and what some people claim to be "neutral/white" for me is already in "blue tinted" category.
You decide which you prefer and then return the other one, and keep returning the replacement until you "win the lottery" and get the specimen you like.