The colors are divided into non-color and color categories. Achromatic colors are black and white, and various shades of gray from darkness to brightest. They can be arranged in a series called the black and white series. The change from black to white in the series can be represented by a gray band. One end is pure. Black, the other end is pure white. The material reflects all visible light, and the reflectance equals 100% pure white; the material absorbs all visible light, and the reflectance equals 0% is pure black. There are no pure white and pure black substances in actual life. The magnesium oxide can only be approximated as pure white, and the black velvet is close to pure black.
The achromatic color of the black and white series can only reflect the change in the light reflectance of the substance, and the visual sensation is a bright change.
When the surface of the print has a reflectance of 80% to 90% of the radiation of all wavelengths in the visible spectrum, the visual sensation is white. If the reflectance is less than 4%, it is black. White, black, and gray objects are not selective for reflections at various wavelengths of the spectrum, and they are called neutral features.