Variable color resolution on LCD displays sometimes makes watermarks disappear

We have been noticing that watermarks do not always show up on different lots of the same monitor model. For example, I have two E172FPb LCD displays connected to a RADEON X300 video card. On the display connected to the digital port of the video card (through an adapter), I cannot distinguish a watermark with the color #F8F8F8 against a white background (#FFFFFF). It looks fine on the display connected to the analog port. Swapping the displays on the video ports does reverse the effect. So I assume the video card is the source of the problem, perhaps because one output is digital while the other is analog. However, we have another computer using a E176FPf display attached to an analog port of a built-in video card (Intel 82915G/GV/910GL) that also cannot differentiate the shades. Neither can one of the E172FPb displays when attached to that computer. Connecting the E176FPf display to the RADEON X300 card doesn't help either. This display can't seem to differentiate regardless of the video card. I have messed with the color settings on the displays to no avail. However, I've noticed that when I use the auto adjust, the watermark shows up for a split second while it is going through its adjustment protocols. However, I'm not sure what it is adjusting and I can't reproduce the effect manually.

 

Has anyone else observed this effect? Is it something that can be fixed? Or is it just something I have to live with?