Spotting

I think the grey look is a peculiar effect of lighting in flight as the perched bird is clearly brown in your first photo, is it the same bird in both pictures? Many bird feathers have the ability to show different colours according to how the sunlight catches them.
There are two sub-species of Yellow-billed Kite in that area, one being much paler than the other, and both used to be considered sub-species of the Black Kite which from my experience can be extremely variable.

Thanks Malcolm. We've seen lots of yellow-billed kites here but none have had that grey colouration on their back. Is this a different variant?

Our guide books say they are typically brown on the back. This one is starkly grey. Looks different.

The forked tail in flight immediately gives it away as a Kite, the barring on the underside of the tail is visible in your first picture and the yellow bill is a clincher, most other raptors with yellow bills have a dark tip.