On Mon, Aug 14, 2017 at 05:47:12PM +0200, Artemio González López wrote:

After deleting the file ~/Library/Colors/Emacs.clr, everything went
back to normal. Thanks a lot for pointing me in the right direction!

I believe you need to delete the file every time you restart Emacs. We
don’t have any other work‐around for this at the moment as we don’t
know why it’s happening.
--
Alan Third