According to this article, there are four possible explanations as to why yellow colour is associated with pornography. Below is a slightly modified translation of the article based on further references from the internet:
Orpiment (雌黃). Orpiment is a toxic orange-yellow mineral that is used as a
pigment by ancient people. Due to poor bleaching technology, paper
produced in the olden days was slightly yellow. When words on a
paper need to be corrected, orpiment can be used to smear onto the
written words, creating a layer of slightly opaque yellow close to
the paper's colour, enabling a rewrite. Soon, people describe
uttering nonsense as "信口雌黃". Subsequently, the yellow colour of
orpiment and its toxicity is later extended to mean poisoning of the
The Yellow Union. In 1887, in a city in France, a factory owner tried to prevent his
workers from going on strike by bribing the Yellow Union. The
workers discovered the betrayal and angrily smashed the windows of
the union clubhouse. The union then used yellow paper backings as a
replacement for the windows. Since then, the workers labelled these
union people as "见不得人的黃色工会”, meaning a union that cannot face the
public, similar to pornography.
The Yellow Book. In 1894, a British magazine
named "The Yellow Book", gathered in a group of conservative collection of authors
to produce quarterly literary periodicals that are thought to be scurrilous in content. Later, a
prestigious Irish playwright, Oscar Wilde, was arrested on
homosexuality charges. At the time of his arrest, Oscar was
seen holding a yellow book (which turns out to be a French novel). People misidentified the material to be The Yellow Book and associated it with his personality. The next day people demonstrated in front of the publisher, and a furry of media reports soon cemented an association between yellow paperbacks and homosexual content.
The Yellow Kid. The end of the 19th century New
York, New York World and New York Journal competed for readers
intensely, posting vulgar comics content to which "The Yellow Kid"
is one of them and is the origin for the term "yellow journalism".
Since then, the colour yellow is associated with erotic and vulgar
There was a time when the color yellow was associated with prostitution also in Europe. For instance, historian Nils Johan Ringdal reports in his Love For Sale: A World History of Prostitution that prostitutes were told to wear yellow scarves in 15th century Vienna. BTW, the book also has a chapter on Tang-dynasty China, but I don't remember further references to the color yellow in there.
There is also a bit more (condensed) information in the Wikipedia article on prostitution during the Middle Ages (German version only): it cites red, yellow, and green as (then) colors of shame.
The Chinese meaning for "yellow " has nothing to do with Pron. In contrast with the English, it has more of the meaning of sexual thoughts, or expressions of sexual content in mind displayed in conversation, non verbal communication. An individual can look yellow, or have yellow thoughts. or say yellow words. In fact in American slang, we would use the word "Nasty".
I can't find the reference now, but I have read that forbidden books in the early Mao era were put in yellow covers after being seized by the police; according to the source, this included both pornographic and ideologically deviant books. I have also seen contemporary Xinhua and other official sources describing banned religious and political texts as "yellow," so it may be used differently in Danghua. However, it is possible the yellow color was chosen because the color was already associated with deviance.
In Hong Kong, brothel and organised prostitute are illegal. It is not allowed to advertise any trade in sex. Brothels and prostitutes hoisted some large yellow light boxes with some red implicit text on it nearby. These boxes were finally taken down by police, and they use a pink light instead nowadays.
In this way, Hong Kong people associates yellow with prostitutes. So do pornography.
Other colours are also being used in recent years.
Nonetheless, I'm not sure when was 黃色 being associated with pornography. The brothels might deliberately choose yellow for reasons explained by 杨以轩, or the use of such signage might have led this association.
Traditionally, yellow is a respectful color in China. It represents nobility and wealthiness. It is the color of the skin of Chinese, the color of the mother river of China. 1934， yellow was decided as the city color of Guangzhou, the capital of Guangdong province.
The negative meaning was brought in from the Commies. They are against Chinese culture. The "People's Republic of China" was originated from "Soviet Republic of China".
黃書is a common usage in Hong Kong. However I am not sure if the usage is originated from HK or elsewhere.