This hue is inspired by the vivid yellow of the maritime quarantine flag—known as the “Yellow Jack.” Historically flown by ships arriving in port to signal the presence of contagious disease such as yellow fever or cholera, the flag’s bright color was chosen for maximum visibility at sea. The term “Yellow Jack” came to refer both to the flag itself and to yellow fever, the disease it so often warned of. In the International Code of Signals, this solid yellow flag represents the letter Q (Quebec), and by the late 18th century, British maritime law required quarantined vessels to fly it under penalty of heavy fines. However, the flag’s meaning has reversed over time: today, a single yellow Q flag signals the opposite—a ship declaring itself healthy and requesting free pratique (permission to enter port). When disease is present, two Q flags are flown together, or the yellow-and-black checkered Lima flag is used. Its bold color endures as a universal maritime signal—once a warning of contagion, now more commonly a request for clearance and safe harbor.