I obtain beautiful greens on silk by over dyeing weld with woad. This green is referred to as Lincoln green, and it is reputed to have been used by Robin Hood and his men.
First, I wash the silk very well and then I mordant it in a 6% alum solution for 48 hours (see WildColours’ pages on mordants). I let the silk dry and cure for a week before dyeing it overnight in a strong weld vat.
I leave the silk to dry for at least 24 hours before washing it well. Then I dip it once or twice in a weak woad vat. Some dyers recommend dyeing the fibre in the woad vat first. If I dye first with woad, then I find it very difficult to control the final colour, which invariably tends to be too blue.