Blues

noun

1. The colour of the clear sky or the deep sea, between green and violet in the visible spectrum, and one of the primary additive colours for transmitted light; the colour obtained by subtracting red and green from white light using magenta and cyan filters; or any colour resembling this.
2. A blue dye or pigment.
3. Any of several processes to protect metal against rust.
4. Blue clothing

   "The boys in blue marched to the pipers."

5. (in the plural) A blue uniform. See blues.