Sounds promising Zeebra, thanks. I got an E-mail response asking me to phone them to discuss this issue with them in more detail. I plan to call them later today.
Shinew, to be honest, your controlled test data is interesting but not very useful, in my case at least. It's interesting to look at even the differences you can see (or at least I can see) between the Amazon Kindle ads. Have a look and compare the background colour of these ~1/2 way down, right margin, where they show off the formatting options screenshots;
K3;
http://www.amazon.com/gp/product/B00...famstripe_kk3g
K4nt;
http://www.amazon.com/dp/B0051QVESA/..._menu_kdptqso3
I think you'll see that the K4 has a much greyer screen, even under the ideal lighting that I'm sure Amazon would have used.