Bad rendering of PNG saved from GIMP

[Tom Mraz]

Hello,
maybe I make some mistake, but when I try to make PNG picture to use it on
my webpage, when I use some color for background of the image and the same
color for the background of the HTML page and then I try to display the page
in MSIE or Mozilla there is a slight difference in the background color of
the image and the background of the page. Is it some error in Gimp? Probably
not, but how could I avoid it?

URL of the example page: http://poli.feld.cvut.cz/~mraz/eps/

Thank you for some help,

Tomas Mraz