there was a post about it im sure can look it up here in jig tiein but the basics is
2 packs kool aid
12 oz water
4 oz white vinger
bring to just under a boild and put what your goin to die in there let it get about 1 shade darker then you want take it out and put under cold tap water
now if its fur like deer tail or tree rat something that i fould the helps befor you hang to dry put betine paper towels and press water out and run a comb thro it helps fur imo

heres a color chart but it shows over darker then white and if you use something white you get a nice true color and you can mix things to get diff looks
Dying Buck Tail