Insecta: Lepidoptera
Erebidae, Erebinae
Erebus caprimulgus

seen at night by torchlight, at rest on a leaf.
Lam Tsuen Valley, Tai Po, Hong Kong.
This is a pretty large noctuid, about 100mm across. There are only a handful of records from Hong Kong, and I think this is the first male that's been recorded in Hong Kong.
The blue around the edges of the wings is light refracted from the camera flash.