The fourth character is the idiom of "emerald green". The last character of the four-character idiom ends with "emerald green" and its explanation:
Cut red dots of green emerald - ①Pick flowers. ②Choose gorgeous words for metaphor.
Love the red and nestle in the green - describes the attachment to the spring scenery.
Gold and emerald green - describes the colorful colors.
Phi Luo Dai Cui - describes gorgeous clothing.
To lean against the red and green - refers to kissing a woman and having sex with a prostitute; having sex with a prostitute.
You Hongyan Cui - a metaphor for the intimacy between men and women.
Even red dots and green - refers to the greased thrush.