Background color is black and comments are highlighted

[ghost]

I'm using iTerm2 and have set background=dark, but the comments are weirdly highlighted and the background is made to be black.

[rakr]

It seems like you are having several issues.

1. the background, try to set termguicolors in your vimrc or init.vim file, this will give you access to the 24 bits colour palette
2. iTerm2 supports italic, but there is a small trick that needs to be applied to make it real, you'll find the instructions here: italics in iterm2 Vim and Tmux