Fyi just found a document just published on the
Samsung lfd site (06-05-2012) called "Development Guide for Prevention of Long Term Image Retention "
In that official document by samnsung you wil read:
Avoid combinations of a text color and background color of contrasting brightness. For instance, white letters with black background may contribute to afterimage burn in more readily than other combinations.
Avoid large areas of gray as this color can very easily result in long term image retention. Please use gray color as little as possible.