Not much is known of the original shirt. It 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.
It is a tight pinstripe patterned "Railroad shirt" with dark navy blue pinstripes running vertically. The shirt had 2 breast pockets and a rounded collar. The buttons are a standard white or pearlescent color.
Eastwood wore his with the shirt cuffs unbuttoned and flipped up.