I didn't think you guys were serious
I had no idea that people actually died their horse's tails. Not sure it's something I would make regular practice but that's me. I'm sure there are better options that dying a tail.
On one of my horse's tails I used to (hasn't been needed with Cobalt his breeding already produces enough mane and tail for 3 horses) along with a few experienced horse owners I know, would condition their tail and vet wrap it all summer. Excellent way of protecting from both the elements as well as allowing to grow (beats any horse conditioner, spray or specialized products).