it looks like a Pinon Imperial Pigeon to me as well. The white at the base of the bill and around the eye is visible if you look closely, it is just that the head is slightly out of focus (the camera is focused on the bars) and the bars themselves partly conceal it.
I stand corrected, upon closer examination I also believe it is a Pinion Imperial Pigeon. Mainly due to the wing feathers, those are very unlike any diamond dove I've ever seen here or in zoos, much more like pinion's in my opinion. (As seen here and here)
Body shape looks wrong for Diamond Dove to me and, based on the mesh, the bird looks way too big for a Diamond. There would also be white dots on the wings (the 'diamonds').
