There are two basic types of dye. ACID and cool-aid. Acid will give you bright saturated color. Cool-aid is more pastel. Cool-aid is much easier.
For cool aid dye. Start with white feathers. First wash cape in warm soapy water...rise well. Heat coolaid in water solution. Turn off heat and insert cape. Let set a while. Color will vary with strength of cool-aid solution and amount of time cape is left in pot. Set color with a mild vinegar solution. Rinse well and allow to dry. Raspberry, lime and blueberry work well.
If it doen't work well...drink the cool-aid!
We chatted a lot on another flytying forum. (SOL) Do a search and it should come up.
Juro ...I hope it is OK to give Gregg this hint?