Why did people in Song Dynasty only wear black and white clothes?

I checked the History of China Clothing edited by Mr. Shen Congwen and the Brief History of Ancient Chinese Clothing edited by Dai Zeng, but I didn't see a similar color-limited description. During the reign of Song Renzong, people were restricted to wear silk and tie-dye due to natural disasters in some areas. It's just a short-term local restriction.

In Song Dynasty, the economy was developed and the mind was more open. China's strict control over the color of folk costumes began in the Yuan Dynasty. The Ming and Qing dynasties inherited the cruelty of strictly strengthening feudal rule and feudal hierarchy and dividing people into three, six and nine grades.

According to the paintings, strokes and other works handed down from the Song Dynasty, the costumes of the Song people are also rich and colorful.