A blue pigment, Prussian blue. / The rich blue colour of this pigment.

plural of boy in blue

A diluted blue hair dye used to reduce the yellowed or translucent appearance of greying hair on older women (because the ability to see the colour blue decreases with age).

plural of powder blue

A signal or process with a frequency spectrum such that the spectral energy density is proportional to the frequency.

the planet Earth

plural of blue film

(Internet) A hyperlink displayed in blue, traditionally indicating that the user has not yet followed the link.

Parapercis colias, a temperate marine fish of the family Pinguipedidae.

plural of blue link