Starting in OS X 10.10 Yosemite, Apple added transparency throughout the user interface, so when you’re looking at a menu, for instance, the color of the background bleeds through slightly. If that transparency makes the text hard for you to read, if you’re taking screenshots for publication, or if you just don’t like it, never fear, because you can turn it off. Go to System Preferences > Accessibility > Display, and select the Reduce Transparency checkbox.