As is shown on our pages, Wailing Cavern pets have alternate skins.
They may have various colors.
Young Venomfang has TWO skins and Cavern Moccasin has FOUR different skins.
Fortune smiled on me, I got Young Venomfang and Cavern Moccasin in the last week.
I've tried to summon/dismiss them for numerous times.
At first, both of them are able to change their skins randomly, just like many other Leashes pets(e.g. red and black skins for Sister of Temptation).
However, Young Venomfang and Cavern Moccasin can not change their skins any more after some hotfixes!
It would be a really annoying change to many collectors...