Black ink refers to a kind of red in black. But before the Han dynasty, it generally refers to blue-green or cyan. In the Zhou dynasty, the word "Xuan" mostly refers to the sky and blue, but in the Han dynasty, it was re-recognized as the true color of the sky, that is, the color of the sun when it sets, just red in black.
Color is a visual effect on light through eyes, brain and people's life experience. People's perception of color is not only determined by the physical properties of light, for example, people's perception of color is often affected by the surrounding colors. Sometimes people also refer to the physical characteristics of different colors produced by substances as colors directly.