Is the background a coloured piece of geometry used as a stage or is it just an horizon or world background colour? If there’s a stage it could be caused by lighting, maybe diffused light from the plane?
If there is no stage, try lowering the camera clipping to just beyond the subject and see if that helps. Just spit-balling ideas here. I don’t know for sure if it’ll help but if it’s not the lighting I’d assume it’s the camera based on the circles being centred. You could probably test this by moving the camera and seeing if the circles move with it.
