To the layman color is a sensation or impression; to the physicist it is a phenomenon associated with radiant energy and wave length; to the lithographer, it is a property of inks and papers which must be given careful study and control to produce a uniformly acceptable product. The psychologists and artists have shown that the three visual dimensions of color are hue, lightness or value, and saturation or chroma. From scientific experiments it is known how these dimensions relate to wavelength and energy, the properties of a specimen measured by the physicist. From the known properties of pigments, dyes and ink materials, the approximate relation between these properties and the visual dimensions of color is known. The physicists instrument for color measurement is the spectrophotometer. Other instruments used for color measurement give numbers that relate in various ways to the visual dimensions of color and the dimensions familiar to the lithographer. An instrument like the author's new Color and Color-Difference Meter, gives numbers corresponding closely to hue, lightness and saturation, but a filter reflectometer or densitometer gives dimensions more familiar to the lithographer. With any instrument, however, it is necessary to know limitations and significance of data if useful results are to be obtained.