Just got a MacBook Pro and the Dropbox icon has been bothering me. Sure enough there was a setting for this! Thanks :D
I wish the monochrome icon for Dropbox would do a better job showing me when the app is syncing or in sync. That's the only reason I still have the color icon.
One approach might be to photoshop hack the color icons to greyscale. They're usually in the resource bundle.
That's a great idea. Thanks for the suggestion.
I found it (and still find it) very weird that Dropbox has an actual setting for choosing the color depth of the icon.