why do grey pixels around black light up

I have two acer al1715smd monitors that I had bought a few months apart. I have noticed an unpleasant effect on the latter model -- the grey pixels that surround black pixels appear white. This causes problems in black-on-gray font rendering. Black-on-white fonts appear sharper, but "skinnier" and difficult to read. ClearType fonts have rainbows around letters. I have created a test pattern that shows the effect. Note the grey lines in between black lines in a vertical pattern show the effect, while horizontal pattern does not.

Here's the picture of the test pattern on the latter monitor:

http://69.203.142.43/~vlad/acer1715smd/effect_on.JPG

And here's the pic of the monitor purchased earlier:

http://69.203.142.43/~vlad/acer1715smd/effect_off.JPG

This effect is present regardless of the video adapter and interface (DVI/VGA) used. I complained to acer about difficulty reading text, and sent it in for repair, but the monitor was returned to me unmodified with no comments.

Does anyone know the cause of this effect? Is it the lcd panel itself, or the electronics. Can this effect be turned off?