What might cause this background "fade" in IE8?

Anybody have any idea what might cause this in IE8? The background is meant to be a solid blue, but as you can see it's not. This is not on my machine and I've been unable to reproduce it, but one of my clients is getting it:

More details: The background is using a png (which it doesn't strictly need to as it's a solid colour, but it's a legacy app so you know how that goes)

Also he says he is getting it on 2 machines in IE8. But all works fine on his end with chrom开发者_运维技巧e and firefox. I also have tried it in IE8, firefox, safari and chrome and they all work fine.

I've come across this. I was using a semi-transparent 1x1 pixel image to overlay some text on a photo and IE8 "created" a fade in the background like your example.

The solution was simply to make the background 2x2 pixels and it works fine.

Hope this helps.