I often work on the same site in different environments, so I built a plugin that styles the admin bar to provide a quick visual reference of which environment I'm in. There's also an optional label (I often use DEV, QA, UAT, and PROD). Or, the plugin can be used to simply colorize the admin bar on the front and back end to match a particular theme or company color scheme. There's a few preset one-click color schemes, or you can define your own. I give you Admin Bar Styler.