Starting in OS X 10.10 Yosemite, Apple added transparency throughout the interface, so when you’re looking at a menu, for instance, the color of the background bleeds through slightly. If you find that transparency makes the text hard 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. While you’re there, click the Increase Contrast checkbox too, and see if you like the way it makes the soft edges of the interface pop out.