Quote:
Woad is native to the steppe and desert zones of the Caucasus, Central Asia to eastern Siberia and Western Asia (Hegi), but is now found in southeastern and some parts of Central Europe as well. It has been cultivated throughout Europe, especially in Western and southern Europe, since ancient times.
They are long used for dyeing textiles and some products... even found as painting, maybe their most famous usage was for warpaint... but with their extremely wide usage on britons, one can bet safely that they are also used as dye for cloth and trousers. As making a paint that only usable in war / battle is non - economic for such large scale.