Why doesn't Mac Mail display the content of an email?

Question

macOS

When receiving a response to a letter, the Mac mail client does not display the contents of the letter, instead a black square. This has also happened in Safari. Sometimes when viewing a photo in Google Photos, some photos are covered in black. How could this be related?

Answer 1

Apparently, this is the mail client.
And, in general, this client forms strange letters on the verge of RFC.
You can try another client and compare.

Answer 2

on one so and on the second poppy everything is fine, strange like that

Answer 3

try changing the color profile of your monitor, it worked for me