Dying it black is not problem. Just get some Synthropol and good black acid dye.These are both available at University Book Store in Seattle so you should have no trouble getting them. Then put the feathers you want to dye into the dye bath made with about 1/4 teaspoon of black acid dye, a good dollup of Synthroprol added to the dye bath (it is both a degreasing cleaner and a dye dispersant, needed to get a good, even dye job) and about 2 quarts of water in a stainles steel pot of some sort. Heat the dy bath to about 140 degrees and add the feathers to it. They should be a nice, dark black in aobut 25 to 30 minutes. Take them out and risnse them with warm water untill the water runs clear and place them on newpaper to dry overnight.
To dye anything but purple, you will have to bleach the feathers white. The Radincitch book on tying classic atlantic salmon flies has a great charpter on dying and bleaching that was written by Ted Roebal, Ph.D. a dye chemist from Seattle. The book shuld be available at Streamside in Issaquah or at Kaufmann's, Avid Angler may also carry it, as may Swede's in Woodinville. It is about $60.00 give or take $5.00. Well worth the money.