flag: Netherlands

The Netherlands' flag, common in tulip, football (Oranje), and cycling-culture posts, though the national color orange famously doesn't appear on the flag itself — that's reserved for the royal House of Orange-Nassau. It's considered one of the oldest tricolors in the world, originally orange-white-blue before the top stripe faded to red through dye instability and was formalized that way in the 17th century.