In Iran it's the colour of mourning whereas in the West wearing something blue is a bridal tradition used to represent love.
In France during the 19th Century blue became fashionable to wear among artists and the general public. Not that this was the influence on Picasso's Blue Period, during which he demonstrated his own melancholy through a series of sentimental and sombre paintings.
I didn't intend to look too deeply into the background of a colour but it's actually quite interesting! And on a lighter note, it definitely has the best shade names...
IKB as it's officially known (although it doesn't quite have the same ring to it does it?)