Reverse icon from white to black, tool or iPhone sdk

I have successfully placed an image into the lefthand ImageView of a default UITableViewCell and this shows up as a white image over the background blue of a se开发者_StackOverflowlected row. However the image is invisible when the table cell background is white.

The image came from a 3rd party iPhone tabbar icon set, hence it is white. Can I programatically flip the image to black? Or is there an Apple Mac icon editing utility that will allow me to apply this change?

(I know some will be tempted to cast this question out to another end-user stackoverflow site but before you do consider that there are 100's or 1000's iPhone tabbar icons on the net and a few developers would probably be interested in adding these to their iPhone App UI outside of a UITabBar.)

Opacity is one of the best icon editing utilities. It has preview modes for how the icon will look on the iPhone, in the App Store, as well as on the web.

Also, Acorn is popular and easy to use.