Achromatic
Without hue: white, black and the greys between them.
Also: colourless, neutral scale
Achromatic means without colour in the sense of hue. White, black and pure grey are achromatic; they differ only in lightness. A scheme of black, white and grey is called achromatic, and it is not quite the same as monochrome, which may use one hue in many strengths. In optics the word has another use. An achromatic lens is built from two kinds of glass so that different colours of light focus at the same point, which removes coloured fringes from the image.