See the very faint yellow tint behind the leg or is it just me?
This looks pretty grey but close up there's an olive tint to the rump area.
This was very noticeable in the field.
The top photo shows the bird's obvious bald patch and the yellow area between the legs, a feature which is somewhat more visible in the bottom photo.
It's either yellow feathers or the birds sat in an egg, or wee or paint or something!!
The obligatory short video.