On Mac computers with Nvidia drivers, pink outlines distant terrain and aircraft against cloudy sky with certain rendering settings.
This is a known bug – the Nvidia drivers that ship with OS X are buggy.
Unfortunately, there isn’t a good solution – Nvidia makes their own drivers for OS X but they tend to kernel panic and destabilize the machine. Changing the GPU isn’t an option since it’s not a desktop personal computer.
You can get rid of them by changing settings, such as not using HDR mode, if desired.