In my dictionary it defines
黃 (Huáng)
- yellow
- pornographic
- to fall through
- surname Huang or Hwang
Imperial China and the robes of the emperor are commonly associated with the colour yellow.
We also have
黃河 - Huánghé - the yellow river
黃山 - Huángshān - the yellow mountain
黃帝 - Huángdì - the legendary Yellow Emperor
So how did the colour yellow come to be associated with pornography?
黃色電影 - Huángsè diànyǐng - pornographic movie
黃色書刊 - Huángsè shūkān - pornographic book
黃色電影
,黃色書刊
/黃書
is a common usage in Hong Kong. However I am not sure if the usage is originated from HK or elsewhere.