Why are fire trucks red?

    The most widely-accepted reason that fire engines are painted red dates back to the 1800s -- a time when there was a lot of competition between the fire brigades of neighboring cities and towns. The firefighters of each brigade took great pride in their pumps. Each brigade wanted their rig to stand out by being the cleanest, having the most brass, or being a regal color. Because red was the most expensive color, that's the color most crews choose to paint the fire apparatus.

     Other sources cite the tradition of painting fire engines red going back to the early 1920's. Henry Ford wanted to make cars as inexpensively as possible and only offered cars in one color: black. With all of these black vehicles on the road, the fire service began painting their vehicles red in an effort to stand out.

     Today, just as you have many more choices of colors available to you for your vehicle, so do the fire engine manufacturers, and it is not uncommon to see white, yellow, blue, orange, green, or even black fire engines, in addition to red. And while some studies hint that colors such as lime-green may be more visible to the public than traditional red, the vast majority of fire departments continue to use red fire engines -- a color instantly recognized by everyone as that of a fire engine.

Source: http://www.scituatefire.org/why_are_fire_trucks_red.htm