@Toki as far as I know in the Indochinese subspecies (Bos javanicus birmanicus) the males don't get really black (I'm not sure if this is the case for all males though), that might be the reason for this coloration.
The other possibility is the animal was castrated/vasectomised after adulthood, which can cause female-type colouration in otherwise classic adult male Blackbuck, for instance.
