Achromatic literaly means "no color" as it designates color perceived to have zero saturation and therefore no hue, such as neutral grays, white, or black.
An achromatic filter in an instrument will have no effect on the color.
An achromatic lens in a video projector has been corrected for chromatic aberration (all colors will have the same focal length). If a regular lens is used, the differing colors will not have the same focal length and "fringing" will occurr. In this image, you can see chromatic aberration in the bottom image, especially in the dark areas on the right side (note the blue fringe).
Achromatic
Linear Mode
