In the past If a discussion page hasn't had any entries , it would appear red. That way we wouldn't click on it thinking that there's some discussion to see. However nowadays the discussion page tab is black just like the article page so we can't tell if it's empty or not. The following picture is of a typical File on Wikimedia Commons which does not have a discussion page yet.
https://commons.m.wikimedia.org/wiki/File:%E8%BB%9F%E5%9F%A4%E5%9D%91%EF%BC%8C%E6%B2%BF%E9%AB%98%E5%A3%93%E7%B7%9A%E5%90%91%E8%A5%BF%E5%8C%97%E7%9C%8B_-_panoramio.jpg
The words file, and discussion, are the same color.