Wash the tail and get it as clean as possible = then dry it thoroughly - then apply the paste to the discoloured hair - and leave to dry _ (I used to leave it on overnight on Ishtar) but make sure it is covered - with a tail bag or I used cling film to stop it getting on her legs.
I would then rinse it off - and the final rinse would have a bit of Reckitts blue bag in it - and her tail would be really clean and sparkling white.
Never had the problem with her daughter Asti - just had to shampoo her well - and her mane and tail was really white. Her hair was totally different from her mums - and her Asti's grand-daughter luckily has the same type of hair as she did.
Reckitts Blue is available on the intranet and is really cheap. I usually wash first in a shampoo for greys and then do a soak in recketts blue in a bucket.
It works fabulously on Fayre and Diva (bearing in mind mine dont get washed all winter!). Jazz's never seems to come up white though so the hair must have different porosity (is that a word?!)
The professional palomino people will be able to give us some good tips for this subject - any of you out there lurking??
Another vote for Tesco value shampoo, just on the ends though. I use insecticidal shampoo on top of tail in summer, then scrub the ends with the Tesco stuff. Finally I rinse with that Supreme Products blue rinse...though as others have cautioned not too much or the tail will be purple. This works for my daughter's very grubby Sec A pony! Lots of interesting advice on here which I may try too in our quest for perfection this summer!
Have tried most of above on one palomino mare and her tail is still stained yellowish. Others come up well with just basic or blue shampoo. Carole, what ratio of Fuller's Earth to hydrogen peroxide do you use? That's one I haven't tried and it sounds like it's worth a go.
I just mix about a two or three heaped tablespoons or so of the fullers earth (which I got off the internet - and it is white )then mix it in a non metallic dish with enough hydrogen peroxide to make a paste. I then smear this onto the stained bits of the tail - and leave it until it is dry (or overnight in Ishtar's case) - then when it is rinsed off - the tail feels really silky. Margaret Coleman who told me about this - was a breeder of Arab's Part-breds and Palominos from years ago. She lived in Sussex - and bred some really good horses. - Can't remember her stud prefix - not sure if it was Lorelei or something like that.