Use the "custom white balance" setting. It allows you to store two settings at a time. I think that in "custom white balance", you point the camera at a white card or neutral gray card (dive slate works), make sure the whole thing is in the picture and then press the OK button before shooting. Learn the shortcuts so that you can do it with a single touch or two at depth. Then reset the white balance if you change depth up or down more than a few feet.