Why can only the emperors of the Qing Dynasty wear yellow clothes?

During the reign of Emperor Kangxi, King Prince Andrew of yi county was the thirteenth son of Emperor Kangxi. He was a prince. According to the specifications of the imperial robes of the Qing dynasty, all the royal robes of the prince are golden yellow, and he can definitely wear them. During the Yongzheng period, Andrew was named the Prince of Yixian, and was rewarded by Yongzheng, so he could be a prince in golden yellow, so the Prince of Yixian could wear a golden robe. About the dragon robe Huang Hongfa was made a prince at the beginning of Yongzheng's reign. According to the etiquette of the Qing dynasty, princes and county kings can wear dragon robes, and Baylor wears embroidered robes for dukes. The dragon on the robe has five claws, and the dragon on the embroidered robe has four claws. However, the robes of the princes of the Qing Dynasty were actually very limited. For example, the number of five-claw dragons and walking dragons is limited. The prince's five-clawed dragons are in front and behind, and the five-clawed dragons are in the left and right. The "dragon robes" of princes and county kings are "supplementary clothes", which means that dragons are not directly embroidered on clothes. But like the minister's royal robes, the patterns are complementary. The one directly embroidered on it is called "Kufu", which is the patent of the emperor. There are also color restrictions, and it is clear that bright yellow cannot be used. This is also the patent of the emperor and queen. The prince's robes can only be apricot yellow, blue, turquoise and so on. Therefore, it is not against etiquette for Huang Hongfa to wear apricot robe, not to mention that he and Yongzheng brothers have deep feelings. Andrew, Prince of Yixian, was posthumously named Prince of Yixian, one of the twelve iron hat kings in Qing Dynasty. He is hereditary and doesn't even have to avoid the word "Yin". In fact, Huang Hongfa's so-called golden robe is not accurate, and it should be apricot-yellow supplementary clothing. In fact, history was buried in the imperial robe, and there were precedents to follow in the Ming and Qing Dynasties. In the Ming Dynasty, when Chang Yuchun was buried, he gave Zhu Yuanzhang a dragon robe. Dourgen was also buried in a bright yellow robe in the Qing Dynasty. But Dourgen's fate is taboo, so Yongzheng's kindness to Huang Tianjun will not violate this etiquette. After Huang Hongfa died, Yongzheng was heartbroken. He ordered Huang Hongfa's tomb to be built into the highest-level tomb of the sovereign in history of qing dynasty, and wrote "Loyalty, Honesty, Diligence, Caution and Honesty" in his own handwriting before Prince Yixian died. Feng is the king of iron hat, which can be replaced by hereditary, and he does not shy away from the emperor's taboo. For example, Yongzheng used three-dimensional characters! These favors are unique in history of qing dynasty.