Why do Chinese paintings often turn colorful things into black and white?

Ink is not only black, it can be mixed with water to produce more colorful changes, and the intentionally left blank after the completion of the picture, often has the role of "white as black", so that the picture is complete and concise.

The ink is dried and blended with water to form a variety of colors, including thick, light, dry, wet and burnt. Thick ink is very thick and black ink, which generally refers to the color of the original ink. Light ink is the light ink color formed when thick ink is diluted with water. Dry ink refers to the brush marks left behind when the brush is accelerated, and can often be used to represent the trunks of cudgels and trees. Wet ink refers to thick and light ink colors that contain a lot of water, and is compared to dry ink. Burnt ink is often the body of ink that remains after the thick ink has evaporated, or sometimes it may form lumps, and is a very dry and thick ink. These five ink colors can express the different textures and "colors" of many objects. For example, to draw a small red fruit, you can dip the brush in light ink, then dip the tip of the brush in thick ink to draw the body of the fruit (which uses both thick and light colors); and then use dry ink to show the fruit stalks, because dry ink must be suitable for the expression of dry and hard texture. This is just a small example, there are many other techniques to accomplish different fruits, for example, to draw leaves you can use thick and light ink to draw a large area of the leaf first, and then use thick and burnt ink to outline the leaf tendons when it is half-dry, in order to better express the texture. Also, ink can be built up continuously so that the black color itself contains rich and subtle layers. Ink has many variations and rich expressiveness, plus ink is an essential and unique painting material in Chinese painting, thus Chinese painting often paints things with color in black and white.