a blog by a guy who's into photography and diving and found this post. Apparently Photoshop has had a white balance, a black balance and a gray balance dropper in their program all along... go to image>adjustments>levels and then look for the droppers in the lower right of the box that opens... whohoo!!!! You can experiment using this on photos that are bluish and get them much closer than you'll likely get them by other means unless you're really talented at Photoshop. I managed to "save" a few old photos in just a couple minutes' time that I couldn't do a whole lot with earlier.
Save your originals! You never know when you'll find out something that'll help you fix a problem you didn't think you could overcome.