[davidmanze]

I had an idea/epiphany (depending on correctness) about the yellow/blue. Probably we are seeing light refraction by the atmosphere, where blue and yellow get refracted at different angles. So we see (lateral)CA, not from the optics, but rather from the atmosphere.

Here an image taken with the Canon EF 600mm f4 L IS USM II:

https://www.the-digital-picture.com/Pictures/Picture.aspx?Picture=2013-09-18_19-25-50

Often, moon images on the interweb are turned black and white (probably to hide colour noise), and so we are not used to seeing that yellow and blue?

A Tamron 150-600mm showing the same effect (but stronger... lower moon probably):
https://www.dpreview.com/forums/post/55573975?image=0

  Yeah, nothing like a nice epiphany moment BC .....

  Ok, it's got to be something along those lines ...... the connection is that when the sun is high in the sky shining down on birds heads causes exactly the same effect. 
 My theory about the darkening blue colour of the sky through branches or in this case feathers "doesn't" hold up for the counter yellow fringe underneath the bird's head.
 
  I've put out the question on the astro photography DPreveiw forum ...... there are a lot of knowledgeable guys there!

Edit:
The first reply says that:
"This is something that an ADC, or Atmospheric Dispersion Corrector would eliminate, although I am not sure if you can get an ADC to fit a regular camera lens. A chap at my astronomy society uses an ADC with very good results on his Meade 16" Schmidt Cassegrain telescope."

A link to this ADC is here:

http://www.star-hunter.ru/en/zwo-adc-review/

Looks to be a unusual bit of kit