Photographing Black and White images, or color images with a primarily white background can present challenges. Often your first try at a photograph can be dark or discolored.
As a first step, take you best shot by setting the White Balance on your camera before shooting; see the White Balance for Color Accuracy tutorial. This will help avoid some color cast and darkness issues.
To correct the raw image:
Astute reader Carrie Jacobson sent her husband's tip for correcting black and white photos that is SO superior to what I posted here that I am removing mine. Click here for the updated version.