PNG, gamma correction and IE7
It seems that not only PNG and IE6 can lead to unexpected difficulties -- PNG displayed in IE7 or IE8 can also surprise one. This is because PNG files can contain gamma correction information, and while most web browsers ignore this when displaying the image, IE7 and 8 do not. This can cause your images not to match the background they have been sliced from, and other unexpected things.
The solution might be to get rid of the gamma correction value altogether, as it is, fortunately, optional. (Or save everything as PNG with the same value.) In older browsers, however, this can cause problems. TweakPNG, as for setting the default background colour, is still a very good solution to edit these pieces of information in PNG images.
Source
The solution might be to get rid of the gamma correction value altogether, as it is, fortunately, optional. (Or save everything as PNG with the same value.) In older browsers, however, this can cause problems. TweakPNG, as for setting the default background colour, is still a very good solution to edit these pieces of information in PNG images.
Source