For the full series see http://tale2tell.com/premiere-pro-tutorials/

In this tutorial, Andrew shows how to use the 'Leave Color' effect as well as a simple compositing technique to be able to focus on just the item needing to be shown without having to worry about similar colours in other parts of your shot. While the 'Leave Color' effect is powerful, it is also a simple approach which may or may not work for you depending on the footage you are working with. If you are not getting the results you want with the 'Leave Color' effect, then you may wish to use the secondary colour correction techniques shown in previous tutorials to obtain a similar and slightly more controllable result