Not So White Tails

I have a Palomino paint, a dirty one, and I am attempting to keep his tail...not brown? Basically if it matched the mane it would be nice, even if it was just a close resemblance. I keep it braided and he is getting a nice tail bag for x-mas, but how do I get it clean?? It's awful looking, I am sure it's stained, I've tried that super white shampoo and it did nothing more than regular shampoo. Is there some sort of trick? At home remedy? Does praying to the deities of light coloured horses help? While he might not give a hoot what colour his tail is, it looks gross and I can't stand it.

Try white vinegar. It cleaned Skipper's tail when I didn't think anything would. I just took a bucket of warm water, added some vinegar and then soaked his tail and rinsed with clean water. His tail was all yellowy and gross. Came out nice although it's back to it's disgusting look again!