It's something with IE rendering the PNG different:
found this:
Inconsistent Color on the Web
When images are used as parts of a Web page design, consistent color handling is often more important than colorimetric correcness. For a design that combines CSS and images, it is important that a color with a particular RGB value is displayed consistently regardless of the source—style sheet or image file—of the color value.
Given the same RGB values, the colors specified in CSS, HTML, JPEG, or GIF have traditionally matched. Everyone has just taken it for granted. (Colors are not represented as RGB internally in JPEG, but everyone uses the de facto color conversion of libjpeg from the Independent JPEG Group.)
PNG breaks the consistency. When the gamma of PNG images is disturbed but the CSS colors are left untouched, the colors no longer match.
There are at least two natural reactions: trying to opt out of gamma “correction” or trying to make it so that the PNG images are considered to be in the same color space as CSS colors.
