Desaturate is a lightweight (sitting at only 195kb) menu bar application for Mac OS X. It lets you toggle grayscale on and off as you so desire without ever having to open the Universal Access pane in System Preferences. And it's free for download too!
I keep my Mac display in grayscale. I actually like it. It's refreshing. Without color, I'm not bothered by things like the blaring red notifications every needy applications employs nowadays. But, syntax highlighting and Netflix still bring me back to Universal Access, where I can deactivate grayscale, more often than I'd like.
Really often, actually. I'm probably Universal Access's only returning visitor. Not to say I enjoy these visits, waiting for System Preferences to load gets pretty tedious when you're opening it forty times a day.
Fortunately, I've come up with a solution, albeit after searching for quite a long time. Most people who've asked about the same thing have accepted proposed AppleScript techniques, which use AppleScript to open System Preferences and select options using KeyEvents. Some others like me tried to use Terminal to change plists and restart WindowServer. I tried to take a new approach. After coming across display tinting software like F.lux that operates by placing a transparent window above all your applications and applying a filter underneath, I came up with Desaturate.
As it turns out, the solution to my grayscale problems is pretty simply: CGDisplayForceToGray(). More sophisticated software can be made to tint your display or even dynamically blur it using similar private API's.
I hope I've helped those few others in the Mac help forums with the same questions as me.