
SPOILER! (Sorry for my bad english). Look at the color of the plumage. Having sex with a poisonous Zhen is dangerous, its fluids, semen and saliva are venomous,. "As they are eyaculated, the poison will be release along with the semen." . and now, read chapter 5. HE EYACULATED THE POISON WITH FEI'S HELP because he decided to lose his poison, decided to stop being a Zhen valued for his plumage and being "beatiful"... then, Chapter 5, page 42: HE IS ALL WHITE! Has been purified from all the poison. in extra 2 finally they kiss and have sex because now they can :

I thojust gh he was all white for.... Other reasonsლ(´ڡ`ლ)

hehe With ejaculation eliminated the poison, Just that. In the extra 2, Caihong does not want to kiss Fei because he does not risk to find out if it really was not poisonous anymore. Her first kiss and first time was in that extra after finding out Fei was okay after the kiss.

His*

I thought Zhen died if they lost their poison?

How is it sad to stop being abused and whipped just because of how humans prize your featherss?

not really. That his feathers were his pride was more a gift to Fei's brother. Fei's brother took care of him, fed him, protected him to make him the most beautiful Zhen but he already died from his illness. The desire to create the most beautiful Zhen was selfish. But Fei wanted to give him another life, to love him not for being a Zhen, not for his feathered beauty. In chapter 5 is when they make their feelings clear.

They not will died. only will lost their color equivalent to the Zhen's pride. but, "pride" is frustrating when they have their heat. They can't be carried away by lust, not be sexually active. It is beauty in exchange for freedom.
SPOILERS
I didn't realize he wouldn't be able to kiss nor have penetrative sex with him cause of the poison ┗( T﹏T )┛