Microsoft's excuse for not fixing PNGs was because nobody uses them.
It took people using them and then adding IE-specific hacks for them to fix them in IE7.
If don't know if IE7 also fixes the colour bug, but if it does then it's just a case of adding this:
code:
<!--[if IE lt 7]>
<style type="text/css">
body {background: url(color_blue.png) repeat-all;}
</style>
<![endif]-->
And then everything is fine.