Not much is known of the original pants. They might possibly have been brought to Spain by Clint Eastwood who originally sourced his wardrobe from local shops in America and from pieces of wardrobe he'd used originally on the series Rawhide.
At first glance many people mistakenly believe that Eastwood wore black or dark blue jeans but the color is in fact a dark navy blue color. They also do not appear to be jeans at all (which are made of denim with typically contrasting stitching and rivets) but rather they appear to be cotton twill pants with a jeans-like pocket arrangement. (Including the watch pocket [aka the coin pocket])