Yes, I agree the underwing is much paler than the standard photos or images of immature Brahminy Kite. But the body is very different also, as the photos show.
This bird is obviously well advanced towards an adult bird because the body plumage is almost adult. Also the underwings are starting to show a rufous colour just about visible on my photos. To quote MacKinnon Birds of China "Immature brownish all over with streaked chest, becoming greyish-white in second year and reaching full adult plumage in third year" which suggests there may be an interim phase between immature and adult. That is why I have suggested this is a second year bird. Perhaps I should call it 'sub-adult' as in this diagram from 'Birds of the Philippines', which shows a very pale underwing.
Anyway, it appears that some immature birds can have very white underwing. If you look at this website, you will see on the bottom line photos of immature Brahminy Kites which are very much paler underwing than your photo.
www.birdphotos.com.au/brahminykiteweb
The final question is - if not a Brahminy Kite, then what is it? The general plumage pattern of body and underwing is very distinctive and only seems to fit Brahminy Kite to me. Plus the size, shape and time of year are more for Brahmini Kite than other species of say Buzzard.
