and denims are really "of Nemes" {de nimes} cloth, from the strong twill made in france. both of the twills were used as sail cloth, and then later at tent cloth-- Levi (of levi jeans) went to california to make his fortune not digging for gold but by selling sturdy tent to the prospectors. supposedly when he got to california he found what the miners wanted was sturdy work pants, one with pockets that wouldn't rip apart when filled with gold, and he made work pants with rivets to hold the pockets on... and so started an industry.

Jeans are (were) most commony blue, because indigo, is a one the few dyes that doesn't weaken cloth, but actually make cotton stronger. (or is it alleged to) most dyes are harmless, its it the mordant that weaken the fibers. indigo uses salt as a mordant.