I've wondered about this for a while. I've got some icons I want to use on my site (arrows for drop-down menus, etc) and I want to change their colors. But they're not one solid color. They have different shades of the same color around the edges so the fill tool doesn't work. Is there a way in Paint.net to change, say, all the green pixels in an image into their corresponding shade of blue or red or whatever?