Why do the buildings in the Forbidden City use big yellow roofs and red houses? Yellow is one of the five colors. The Book of Changes says, "Heaven is mysterious, but it is like rehmannia". In the ancient theory of Yin-Yang and Five Elements, the five colors are matched with five sides and five elements, and the earth is in the middle, so yellow is the central positive color. The Book of Changes also said: "The gentleman Huang Zhong is reasonable, in the body, in which beauty lies, in the four branches, and in the cause." Therefore, since ancient times, yellow has been regarded as the orthodox color in the middle position, and the neutral color is regarded as the most beautiful color. The yellow robe became the emperor's special costume. In 960 AD, Zhao Kuangyin, the general of the Later Zhou Dynasty, led an army to war. The generals took the opportunity to hold him as emperor, dressed him in yellow robes and became the first emperor in the Northern Song Dynasty. The path taken by the emperor is in the center of parallel lines, which is called the ecliptic; Yellow is associated with the emperor.

Red is also one of the main colors. Humans have known red for a long time. Sui Lian invented the lighter, and people began to understand cooked food. This is an amazing evolution. Fire is red, so is the sun in nature. Archaeologists found red shells and animal teeth in caves where Neanderthals lived, which were judged as the earliest decorations for human beings. This shows that human beings not only know red, but also regard it as a beautiful color. Red is related to human life, giving people hope and satisfaction, thus giving people a sense of beauty, so people will regard red as a festive color; According to the regulations of the Ming dynasty, all memorials dedicated to the emperor must be red, which is the so-called little red book. The Qing dynasty also had a similar system. All the chapters approved by the emperor are wholesale by the cabinet in Bamboo Book, also known as the red edition. From this point of view, according to the etiquette system of feudal society, it is inevitable that the Forbidden City takes yellow and red as the main colors of the building.

Yellow and red are the main colors, but how to organize and arrange these colors depends on the content and purpose of architectural art and the artistic skills and level of designers. The Ming Dynasty ended Mongolian rule and unified China, which was ambitious. Zhu Yuanzhang, the first emperor of Ming Dynasty, took Nanjing as his capital, and planned and built the imperial city and Miyagi on a large scale at that time. Judy, the founding emperor of the Ming Dynasty, moved to Beijing and rebuilt the Forbidden City on a large scale on the basis of Miyagi, the capital of the Yuan Dynasty. The emperor's demand for palace architecture is naturally that the overall spirit should be great, the building should be gorgeous, and the power and majesty of feudal emperors should be reflected as much as possible. In order to meet this requirement, in addition to the planning and layout of the building, the combination of spatial changes and the shaping of the architectural image, the contrast method is also applied in the architectural color.

In chromatics, contrast refers to cold and warm contrast and complementary color contrast. In painting, red and yellow are usually called warm colors, while blue and green are called cool colors. The so-called complementary colors mean that when two colors are mixed and superimposed into white light, and two colors are fused together to become gray-black, these two colors or colors are called complementary colors, such as red and green, yellow and purple, blue and orange. Putting cold and warm colors or complementary colors together can set off each other, making it more lively and the effect more eye-catching. And because of the adjustment of human vision itself, the two contrasting colors are neutral and balanced.

This contrast rule is widely used in the architecture of the Forbidden City. Under the blue sky, with a single yellow glazed tile roof, with turquoise painted and bright red palace walls, stone pillars, doors and windows, and with white stone foundations and dark ground, blue and yellow, green and red, white and gray-black form a strong contrast, resulting in an extremely bright and magnificent overall color effect of the palace building.