On older lenses, “Color” usually referred to suitability for color film, and was often at least partly a marketing label from a time when color film was less common.

There can also be a technical angle: color film makes chromatic aberration much more obvious, because different wavelengths can focus slightly differently and show up as colored fringes. In black-and-white, that same issue is harder to notice and may appear more like a slight loss of sharpness. So a lens promoted for color use may have had better correction for chromatic aberration, or the maker may simply have wanted to emphasize that it was appropriate for color photography.

That doesn’t mean such a lens is only for color, or that a non-"Color" lens is unusable with color film. In general, the same lens can be used for both black-and-white and color film. A lens that looks fine on black-and-white can appear worse on color if it has visible chromatic aberration, but it will still form an image normally.

By modern standards, essentially all lenses are expected to work well with color capture, so this naming has mostly disappeared.