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