Hi, PJ. I can tell you how to lighten some stains but, just so you know, you will not be able to remove color selectively. You will have to try to get the color as close to the original wood as possible.
There are dye based stains and these react to bleach. There are pigment based stains and these react to oxylic acid. But most stains are a combination of the 2, to some extent or another. A brief explaination of the process was previously given on this board at "Lighten walnut stained oak kitchen cabinets" by Cheryl on July 15. You might also search for info on this at www.citristrip.com and then Ask the Experts. Whatever you do, wear gloves and eye protection when using any of the chemicals mentioned.