High Sierra update: This trick no longer works in High Sierra. As far as I know, there is no workaround.

Here's my first (only?) Yosemite hint, courtesy of my Many Tricks partner, Peter Maurer. Peter wanted a light menu bar, but preferred the contrast given to application icons in the dark Dock—like this:

Here's how to achieve that effect.

Open Terminal, then copy/paste this and press Return: defaults write NSGlobalDomain AppleInterfaceStyle Dark Paste or type killall Dock and press Return. The Dock will relaunch in its dark mode. Copy/paste this and press Return: defaults remove NSGlobalDomain AppleInterfaceStyle

The first step sets dark mode, step two restarts the Dock to switch it to dark mode, and step three turns off dark mode—but the Dock won't notice, and will remain in its dark state (until it's next restarted, which isn't often). Because the Command-Tab switcher is associated with the Dock, it will also be dark.

If you're going to script this, you'll want to insert a delay between the second and third steps, so that the Dock can finish launching before you disable dark mode. Neat trick!