His white chin hairs are a prominent feature within his family line. Shikamoo and Sule have them too (while males like Furahi lack them). It may be a feature of Snowy’s line as I have an old photo of Mahinga (1996-2005) at Wellington as a juvenile and he has them.
@Zoofan15 Quite a common 'verus' trait, definitely seems to be a feature of this particular family line. I'd be very interested in seeing your old photos of Wellington's chimps!