According to local legend, the town was on a busy stage coach between Dayton, Ohio and Cincinnati, Ohio along the Dixie highway, but kept being passed by because most stage coach drivers were illiterate and could not read the sign with the town's name on it. So, in 1862, the town council changed the municipal name to reflect a landmark, a blue-colored metal sphere that was suspended above the intersection of the two highways at the heart of town. A modern successor to that blue ball still hangs on Dixie Highway.
Blue is used also as a word to denote a sad or melancholy state, as in depression, or simply a state of deep contemplation (however, the phrase "blue skies," referring to sunny weather, implies cheerfulness).
Blueballs is a slang term for a temporary fluid congestion in the scrotum and prostate region.
Blue is associated with many air forces and navies because of the color of their dress uniforms, while green is associated with armies.