Blue is the colour of light between violet and green on the visible spectrum. Hues of blue include indigo and ultramarine, closer to violet; pure blue, without any mixture of other colours; Cyan, which is midway in the spectrum between blue and green, and the other blue-greens turquoise, teal, and aquamarine .

1 : of the color whose hue is that of the clear sky : of the color blue (see blue entry 2 sense 1) a blue jacket her bright blue eyes The house is blue with white shutters. 5 of a woman : learned, intellectual … the ladies were very blue and well-informed … — W. M.