I guess you could read the descriptors of "naked and hairless" and "human-like" to imply that you should paint your tirapheg in normal human skintones. That strikes me as a super-creepy option. But the fact of the matter is that we don't know for sure. The original vision of the tirapheg could look more like one of these:
And don't worry about the fact that an official mini of your monster doesn't exist. Even a DM like me, who rarely uses figures and can't paint his way out of a paper bag, can do a little kitbashing if the situation call for it. It only takes a small plastic lobster from a zoo gift shop, the wings off of a plastic dragon fly, a toothpick, and a bit of paint to make a garbug, for example. Heck you could fake the wings with cardstock if you wanted. A tirapheg probably wouldn't be too hard to mock up out of Sculpey or you could hack together parts from a couple of Reaper sculpting dollies.
|No offense to whoever at Games Workshop|
sculpted this unreleased tirapheg figure, but I
figure a lot of people could do at least this well.