This panel is mostly about how things look on the screen: windows, menus, buttons, scroll bars, and fonts. (It used to be called Appearance, but General is more like—yes, you guessed it—the iPhone and the iPad.)
These pop-up menus let you crank up or tone down OS X’s overall colorfulness:
Appearance. Choose between Blue and Graphite. Blue refers to OS X’s factory setting—bright, candy-colored progress bars, menu, and pulsing OK buttons—and those shiny red, yellow, and green buttons in the corner of every window. If you, like some graphics professionals, find all this circus-poster coloring a bit distracting, then choose Graphite, which renders all those interface elements in various shades of gray.
Use dark menu bar and Dock. When you turn this checkbox on, the backgrounds of your menu bar and Dock turn dark gray. Here again, Apple probably had visual artists in mind with this feature—but it looks cool and calming no matter who you are.
Automatically hide and show the menu bar. This checkbox has nothing to do with colors, of course. But it’s a new El Capitan feature that can make a big difference on a small screen (this means you, laptoppers).
When it’s turned on, your menu bar disappears (including the menu-bar clock and other menulets). It reappears only as needed—when you move your cursor to the top of the screen.
Highlight color. When you drag your cursor across ...