You can use png masks to create an icon, and then change the background color of the element below it. You can also use image scaling to make the icon any size you need.

http://www.cssbakery.com/2009/06/background-image.html

SenchaTouch does this for all their button icons.

The downside is that you can't use spritesheets, because each image needs to be inserted with an image tag, not a background image.