[Redys]

well i think i may have hit the nail on the head

i took a picture of the whole site with print screen, opened in photoshop and then went with the color selector in different places. the background is the right color on the page and on some of the pictures. however, unbelievably, some of the other pictures have a different background color!
the difference is the background value end ins AB, and the other pictures some end in AA, some in AC, some change some numbers too, but all very minimal. it still doesn't explain why in all these other computers the difference is so minimal that nobody had noticed it except on the MAC...but it's a start...