if tuye saw him without his mask, wouldnt he find out he's a normal deer?
I made a mistake saying "sibuxiang's face" when I should've said "those who know qilin sibuxiang will always recognize him as having white fur, those who don't and only know deer sibuxiang will see him as having yellow/orange fur"
Tuye only sees sibuxiang as a deer wearing a mask as he has never seen the qilin version of sibuxiang. The first time they interacted was when they were drunk in a bar in the modern era and that was long after the time sibuxiang recieved his mask.
Also to note is that he thinks that moment was a dream.
There was a moment in the story when he described sibuxiang's fur as being a beautiful yellow/orange (not sure which colour exactly) but never has described his fur as white.
Sibuxiang is also not a normal deer, he is a deer spirit just like how meimei is a fox spirit. He was given the mask made from sibuxiang after coincidentally being at the scene and also had his skeleton replaced with the qilin sibuxiang's skeleton which is probably why he can ride auspicious clouds.