tpaksu

This plugin uses CSS technique to fix the png image transparency issue and jQuery to apply this script to all of png images shown in the page. 
This doesn’t work for positioned and tiled png background images. Maybe in next versions.

WP pngfix

Plugin that fixes the png image transparency issue on IE.

Steve Kimpton

Continuously and gently changes color of background and/or pictures with transparent areas on selected pages.
This plugin starts with the custom background (or a fixed color for themes that do not 
provide a custom background) and gradually modifies it in a color wheel fashion to selected pages. 
Pictures on those pages that contain transparent areas may also be set to receive this 
background color.
See a live demo at <a href="http://wordpooldesign.co.uk/wordpress/dynamicbg" rel="nofollow ugc">http://wordpooldesign.co.uk/wordpress/dynamicbg</a>
A settings screen is provided under Dashboard > Appearance > Dynamic Background and also from the toolbar.
<h3>Credits</h3>
The javascript file getbg.js contains functions that convert hsl to rgb and the reverse. This functionality can be found from several sources but mine were from Garry Tan (<a href="http://axonflux.com/handy-rgb-to-hsl-and-rgb-to-hsv-color-model-c" rel="nofollow ugc">http://axonflux.com/handy-rgb-to-hsl-and-rgb-to-hsv-color-model-c</a>) who credits mjijackson.com (this link no longer works) but it seems the ultimate source is the information in <a href="https://en.wikipedia.org/wiki/HSL_and_HSV" rel="nofollow ugc">https://en.wikipedia.org/wiki/HSL_and_HSV</a>

Dynamic Background Colour

Continuously and gently changes color of background and/or pictures with transparent areas on selected pages.

WP pngfix vs Dynamic Background Colour