Strongbow,
The Rit that I used recently for dying linnen bowstrings said to use salt in the mix, to set the dye, if using on natural substances. It also said you had to wash after dying, with a gentle dettergent, like dawn dish-soap. The green and black were good after one wash, but the red was bleeding onto my hand until I washed it four times, and then it still bled with heavy handling. It also faded the color, a little. If the dye is coming off the feathers, maybe somebody else could advise you on what they'll take in the way of washing. I am just now doing my first arrows, so no clue, here.
dogleg