Like is said in a previous post on this thread, you have three choices for cleaning any feather or fur for dying: 1) use clear Ivory dish Detergent; 2) use Veniard's Venpol; or 3) use Synthrapol. Synthrapol is best followed in order by Venpol and lastly Ivory Clear Dish Detergent. Wash the material in a bath of the Synthrapol (or one of the others) and rinse it throughly in cool water. Then place some Synthrapol (or the others) in the dye bath itself to keep any gease and dirt suspended and also to promote even dying of the material.
Yes, you must bleach dark colored materials in order to dye them unless you are looking for a specific overdye color (I do not recommend newcomers to dying do overdying or mixing of colors). And you can nevery use household or other clorine bleaches to bleach feathers or fur because it will dissolve it and ruin it. You must use 20% Peroxide (available only at beauty supply shops, not drugstores) and Lady Clairol Professional Hair Lightener (again this is only available at beauty supply stores). Mix the Peroxide and the hair lightner according to the directions on the hair lightener box and you can bleach virtually any material to a very light tan or ecru, which can then be dyed narly6 any color you desire except for very light egg-shell blues, very light pinks, or light yellow.
And use acid dyes for your dying because they have been formulated specifically for use with protein-based materials and acid dyes will always dye to exhaustion (meaning all or nearly the dye is absorbed by the material with little or none left. The acid dyes allow you to simply put the material in the dye bath and do nothing for 25 to 30 minutes. At which time, the material is dyed and the dye bath can be dumped into a colander for draining and rinsing in cool water.