Getting its name from uniforms of the British Royal Navy, navy blue is a deep, dark blue that’s almost black. Some shades of navy, such as the Web color navy, are a bit bluer.
When this color name, taken from the usual color of the uniforms of sailors, originally came into use in the early 19th century, it was initially called marine blue, but the name of the color soon changed to navy blue.
An early use of navy blue as a color name in English was in 1840 though the Oxford English Dictionary has a citation from 1813. Wikipedia
Carrying the blue symbolism associated with the darker shades of blue, navy conveys importance, confidence, power, and authority as well as intelligence, stability, unity, and conservatism. Like black, it carries a sense of elegance, sophistication. It’s associated with police and military. (About.com)