I disagree - I don't think there is any blue on this bird. I think the way the light is falling on the coverts make them look bluer. In addition, a young male blue-and-white would show blue on the primaries and tail.
Overall, the bird gives the impression of being smaller than blue-and-white. Other features include a large eye, short pale legs, orange wash on the throat, pale lores, pronounced eye-ring and strong rictal bristles around the base of the bill. Overall I think this bird gives the impression of a female Hainan Blue.
This is a migratory species so it would be surprising if it didn't occur on Po Toi, at least occasionally.
