As the other replies to this post indicate, it is best to get the exposure and white balance correct when the
image is captured...however, many times an image can be improved with simple to use (and free to download)
software. My favorite is called Irfanview (www.irfanview.com) besides many other features, under the Image -->
Color Corrections menu, you can change the amounts of red, green, and blue hues as well as saturation, gamma,
and contrast - most of the images I have just need a little more red or blue to make the white background look
right. Give it a try - it's free unless you decide to make a donation!