Discolored gray sections of wood are best repaired by replacing them. This is usually not an option though. Bleaching will leave you with a lighter shade of gray and rarely ever does what people expect it to do. Bleaching actually removes the color and can damage the structure of the wood. Not to mention, it stays active in the wood for longer than you think. Bleaching will, however, lighten most of the wood to a uniform gray that is stainable. You have to bleach all of the wood to achieve a uniform look and at best, YOU WILL still see the stains. Most people after bleaching or after water damage, will paint. White washing may give you a nice "pickled" finish, but the pickled finish is a hard finish to do on wood that is not sanded well.
Maybe you should consider staining with a dark stain that will mask some of the gray.
Tom in KY, Sealing both sides of the wood before istallation will slow the staining if a leak occurs. NOTHING will stop water damage completely.