Feathers are basically hair so anything that will work on wool will work on the feathers.
Madder root....red, rust, peach colours, if you add iron to the dyebath you'll get maroon colours.
Onion skins = bright yellow
, though it will fade fairly quickly to a soft butter yellow. Add alum to help fix the colour and add bicarbonate of soda to brighten it. Weld or Golden Rod will also give good yellows quite easily.
Woad....will give good blues, stinks to high heaven though and is a bit of a bother to get it right, but really worthwhile colours.
Green can be really easily done if you dissolve some copper in ammonia...this liquid is TOXIC and must be handled with care.....
Dye take up will be greatly influenced by how greasy the feathers are, I suggest you wash them first in either Fairy liquid or shampoo (hey, it's meant for hair
)
If you then mordant them the dye will really fix to the feathers.
About 70% of British dyestuffs will give yellow, if you add iron, it will sadden the colour and give it green tinges, if you add copper it will give brighter green shades or deepen reds and rust dyes.
The other mordants commonly talked about are Chrome and Tin......both are horrendously pollutant of water systems, please don't use them, the colours you can get without poisoning our environment are really good anyway.
If you'd like some of the dyestuffs I've mentioned PM me.
Cheers,
Toddy