Blue – The common colors of Blue was produced by using a cheap dye used for Roman Clothing.
The cheaper colors of Yellow were produced from Woad. Woad was a European herb (Isatis Tinctoria) of the mustard family, grown for the Blue dye stuff yielded by its leaves – cultivated as a source of Blue dye.
The leaves were dried, crushed, and composted with manure. The dye was produced through fermentation over several weeks.