(Science: microscopy) Literally, colour-free. A lens or prism is said to be achromatic when corrected for two colours. The remaining colour seen in an image formed by such a lens is said to be secondary chromatic aberration.
a truly achromatic lens would transmit light without decomposing it spectrally and there would be no colour fringing in the image. A doublet, composed of a positive and negative lens element, can be made achromatic for two colours which much improves the performance for most of the others. Being of the achromatic color of maximum lightness; having little or no hue owing to reflection of almost all incident light; as white as fresh snow; a bride's white dress.Being of the achromatic color of maximum darkness; having little or no hue owing to absorption of almost all incident light; black leather jackets; as black as coal; rich black soil.Having no hue.A substance that is either colourless or is resistant to staining agents.