IIRC, IE renders the colours of a png slightly differently to everything else (god knows why, perhaps something todo with ignore alpha channel data).
So, you have two options, either stop using png, and use a different format, or use some php code to detect the browser (using the useragent) and display a different image depending on what the browser is.
Don't build two different sites, just have two versions of the image, and simply output different html.
Google for "php browser detect" or something along those lines for some code
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