I love my palominos, but those tails! If I haven't kept them bagged faithfully and need them to be pristine, I mix a paste of Oxi-Clean and bluing and apply to the ends. I never let it touch skin. I leave on 5-10 minutes, rinse, and condition like crazy. I use the bluing alone if it is on a weekly/regular basis or on my one horse whose tail isn't all a bright white.
I use a little full strength ezall shampoo first to get all of the dirt & stuff out of my palomino's tail and mane. It's amazing how much whiter it looks with just this. Next I use a bluing shampoo leaving it in for about 5 minutes to whiten. Last I use a good conditioner.