I just returned my first K4 for a replacement. Amazon overnighted to me free of charge. My first one had a gray cast to it so much that when it ghost it was white ghosting not the other way around. the CSR said he never heard of one doing that so he gave me another one.
The new one has a light gray background to it. It's much better then the one I returned. Not as light of a background as my K3 which is a creme but pretty darn close.The text is much blacker on the new one as the old one was a dark grey.
So if you get a K4 with a really bad gray cast to it, just exchange it. It's not suppose to look that way.