It is interesting to note that green was an expensive color until the advent of synthetic dyes. There are natural dye sources that dye greenish but none that truly make a green. Instead you have to dye the yarn or fabric twice – once in indigo/woad and once or twice in yellow. Since indigo based dyes sit on the fiber and are not chemically bonded the same way most dyes are, it is tricky to know what order to dye. Do you potentially contaminate the indigo bath with yellow fabric or do you dye blue first and then dye it yellow? It is an interesting problem. I have found that dyeing blue over the yellow creates a blue fabric. Dyeing yellow over the blue I think dyes the indigo particles and thus yields a better green.