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.
A blue dye or pigment.
verb
To make or become blue.
To treat the surface of steel so that it is passivated chemically and becomes more resistant to rust.