Achromatic
From The Glossary of Digital Photography
(1) Without color. An achromatic lens will refract all colors equally, which means the lens has no chromatic aberration or is corrected for chromatic aberration by the use of multiple lenses to focus all colors to a single point. (2) Refers to the colors of black, white, and some grays, which are really noncolors since they have no hue. See also chromatic aberration
