[davidmanze]

It anyway seems to be a minor oddity. I think I'd love this lens to death anyway. If it had an EF mount, of course ;-)

    Here is a review of the lens where I found showing exactly the same effect on a half moon shot!

 https://www.camerastuffreview.com/en/nikon-lens-review/review-nikon-af-s-600mm-f-4e

[Brightcolours]

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

[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

[Brightcolours]

  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

Which photo will show the bird issue?

[davidmanze]

  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

Which photo will show the bird issue?

https://www.flickr.com/photos/124690178@N08/48744067896/in/dateposted-public/

https://www.flickr.com/photos/124690178@N08/48743578508/in/dateposted-public/

https://www.flickr.com/photos/124690178@N08/48788020352/in/dateposted-public/

  Both of these shots had a blue fringe on the top edge of the birds head for example, (you have to zoom plenty) ....... not so easy to see on Flickr. 
Most of the images that suffered from the effect were also spoiled by troubled air and as a result are deleted.

[Brightcolours]

I am not seeing anything "optical" there... The 1st image shows stuff that has to do with the conversion software method, (over)exposure. Your eyes want to see "blue" in the white fringe. What do they see above the beak (yellow)? Do a 300% pixel peep and you will see what I am trying to get at.
The 2nd image shows a lot of noise reduction, (blotchy OOF green bokeh shapes), so it makes no sense to study that particular image for optical or not artifacts...

By the way, the 1st image ALSO shows a lot of NR, even though you have a D500 and images should not need any NR to begin with (although I can't see which ISO setting you used). So first get to grips with the conversion side of things? ;-)

Is this (conversions) done by Lightroom? I can't imagine all the NR crap and artifacting is introduced by flickr...

Here a 400% pixelpeep for your consideration:

  600mmcrapsoftware.jpg (Size: 48.68 KB / Downloads: 4)

Green line around areas where few blue pixels pop up, they are from the used demosaicing algorithm used, going from white to dark and taking some wrong guesses. Between those blue-ish results you can see a redish result in the magenta line, also from the same demosaicing algorithm. You are using a bayer pattern CFA sensor after all.
Around the whole edge is a ghost edge, in "white" as seen within the red line, and as seen in "yellow" within the blue line.

Ah, you added a 3rd image.

To me, that too looks like CFA conversion stuff, the bright white and hard edge to the darker green making for some "odd" demosaicing/interpolating choices and a blueish pixels as a result.

[davidmanze]

I am not seeing anything "optical" there... The 1st image shows stuff that has to do with the conversion software method, (over)exposure. Your eyes want to see "blue" in the white fringe. What do they see above the beak (yellow)? Do a 300% pixel peep and you will see what I am trying to get at.
The 2nd image shows a lot of noise reduction, (blotchy OOF green bokeh shapes), so it makes no sense to study that particular image for optical or not artifacts...

By the way, the 1st image ALSO shows a lot of NR, even though you have a D500 and images should not need any NR to begin with (although I can't see which ISO setting you used). So first get to grips with the conversion side of things? ;-)

Is this (conversions) done by Lightroom? I can't imagine all the NR crap and artifacting is introduced by flickr...

Here a 400% pixelpeep for your consideration:


Green line around areas where few blue pixels pop up, they are from the used demosaicing algorithm used, going from white to dark and taking some wrong guesses. Between those blue-ish results you can see a redish result in the magenta line, also from the same demosaicing algorithm. You are using a bayer pattern CFA sensor after all.
Around the whole edge is a ghost edge, in "white" as seen within the red line, and as seen in "yellow" within the blue line.

Ah, you added a 3rd image.

To me, that too looks like CFA conversion stuff, the bright white and hard edge to the darker green making for some "odd" demosaicing/interpolating choices and a blueish pixels as a result.

   Via Flickr is not the best situation but maybe........ I'm not imagining any of it, some have had a clear blue fringe like the moon shot......... but I have 10 TBs of memory nearly full so anything poor is quickly deleted. As soon as I find an appropriate example I will post it!