Guides in illustrator appearing faint

As the title suggests, in Illustrator, my guides seem extremely faint. I've tried resetting my preferences and also uninstalled and reinstalled Illustrator on my Mac. This problem only recently appeared within the last week. I've tried opening new files and the problem persists. Here's two screenshots that show the same file open on my desktop and my colleagues. I'm sure I'm missing something simple but would appreciate knowing what that is. Thanks