Here is a quote from FAOL (Fly Tying site by Jim Smith)...
"Dyeing your own feathers and fur is often the only way you have to get the exact colour you want for that special pattern or even that old traditional that you want to tie. If you use a well proven dye like Veniards fly tiers dye it is not difficult or messy and can develop into an interesting pastime for when you are not at the fly tiers bench."