The primary colors of light can be blended in a certain proportion to give various colors. According to the research,the three primary colors are red, green and blue (It is like the red, green, blue color of pigment). The screen of color TV is made up of small dots of red, green and blue. The colors are mixed in different proportions and strong and weak colors, which can produce various color changes in nature. Pigments and other non luminous objects of primary colors are magenta (equivalent to rose red, pink ),green (equivalent to deep blue, blue),yellow) (equivalent to lemon yellow). Selected by the British chemist Fraser Bo West (1781 - 1868), a variety of colors can be mixed by the primary colors , but black can not be mixed. Therefore, in color printing, in addition to use of three primary colors, also need to add black, to get a deep color.