For many years I believed that blue dun was some kind grey but now I know that it isn't green. I'm educated now.
We have at least one old topic on this. Very old. Go on - find it! IIRC it includes blae and bloa too.
Some substitutes from Flyhookfiller: Blackbird sub, male and female, old stock from Veniard. http://www.flyhookfiller.se/flugbindningsmaterial-flugbindning/flugbindningsmaterial-flugbindning-fjader/blackbird-koltrast/7-109.html Male. http://www.flyhookfiller.se/flugbindningsmaterial-flugbindning/flu...