mixing the veniard dyes is a no no! there all made up of three different colour dyes already, there a nightmare to mix and never the same.
your better off buying the colours, there easy to use just add it says a 1/4 of a teaspoon per litre of water but i put a 1/4 or so of a teaspoon in 2 3rds of a litre and that will dye plenty of feathers,dubbing whatever....
you fix the dye with white vinegar after you simmer the materials, keep them moving and checking them. also iv noticed the dyes set at different rates sometimes you need to simmer them then leave to cool down in the dye bath.
but remeber to keep checking they can change richness in seconds

theres colours iv dyed that you cant get elsewhere so it is worth experimenting. what is it you want to dye?