It's a Widget in the Widget dock. The icon's color signifies the active or inactive state of the Widget. An active Widget is a Widget you've opened before. These icons have color in them. An inactive Widget is a Widget you either have never opened or have closed. These icons are grey-toned.

The Widget dock has two forms, collapsed and expanded. These two forms show different sets of Widget icons. The collapsed dock shows color icons for active Widgets only. The expanded dock shows both color icons for active and grey-toned icons for inactive Widgets. You can switch the dock between the collapsed and expanded forms. Just move the cursor over the dock to make the head appear, and click +.

The expanded dock serves as a menu for the standard set of widgets as well as any Widgets you've closed. To open or re-open a Widget, just click its icon in the dock.