There are several versions of brothel in history. One refers to a woman's boudoir, one refers to a blue house, and another refers to a restaurant where literati discussed poetry and Taoism. Nowadays, when we talk about brothels, most of them think of brothels, which are known to be dirty places where filth and evil spread. However, in ancient times, brothels were not like this at the beginning.
In ancient times, the requirements for women were very strict. In addition to being able to leave the house when they got married, they usually stayed at home. Especially for girls from wealthy families, the etiquette is extremely strict. Every day, the girls sit in their boudoirs and pass the time by reading porn or poetry, because the girls living in the boudoirs are all in their 20s and 80s. Young girls, so over time, the girl's boudoir was called a brothel.
Secondly, cyan was a very noble color in ancient times, not only because of the difficulty of refining it, but also because of the meaning it represented. Class divisions in ancient times were very strict. There were regulations on what kind of clothes should be worn by what kind of people, and what colors and patterns should be used. In order to show their status, some dignitaries would paint themselves with cyan paint. A house for living, and people also call such a house a brothel.
Also, in ancient times, many literati often held poetry gatherings, especially before the annual imperial examinations, when students from all over the country gathered together. Some smart businessmen saw business opportunities in this, so they specially built a restaurant for these scholars to chat. In order to make the restaurant recognizable, they named it Qinglou, which means Qing in three o'clock water, which means the inside of the building is pure and clean. The receptionists were all literati. Such restaurants were naturally very popular, and later imitators also did the same. However, due to inaccurate information conveyed in ancient times, they gradually evolved into brothels.