Aqua is a trade name for the GUI of Apple Computer's Mac OS X operating system and the primary theme used in this GUI (the other theme being brushed metal). It is based around the theme of water, as its name suggests, with droplet-like elements and liberal use of translucency and reflection effects. As a theme, Aqua is the successor to Platinum, which was used in Mac OS 8 and Mac OS 9. Much of Aqua's original design was intended to complement the look of the original plastics of the iMac and Power Macintosh G3/G4 desktop models, but as Apple has moved to the use of brushed metal in their industrial design, Aqua itself has changed to incorporate the additional brushed metal look. This somewhat inconsistent mix of interface styles has been controversial among the Mac OS X user community.
Two primary features of Aqua are the gel-like buttons (colored red, yellow, and green) that control the windows, and the Dock, which facilitates the launching of and navigation between applications.
The two main styles of windows that Aqua includes are the standard pinstriped and brushed metal windows. Both the standard pinstriped windows and the brushed metal windows appear to have the navigational buttons sunken into the window, however in versions of Mac OS X prior to 10.2, the buttons appeared to be on top of the pinstriped windows. Brushed metal windows also have more plastic-like buttons. Mac OS X also allows users to choose a Graphite version instead of an Aqua version of the interface. (In Graphite, window controls appear silverish-grey instead of red, yellow, and green.)
Over successive releases, Aqua has been toned down to become more subtle. For example, the pinstripes have become fainter, system dialogs and menus have become less aggressively translucent, and the look for buttons and other widgets has become slightly softer.
Aqua is powered by the Quartz Compositor, which handles the underlying graphics management.
The Aqua GUI made its debut in Mac OS X's Developer Preview 3 ("DP3"), demonstrated at the February 2000 MacWorld Expo in Tokyo. Aqua's first appearance in a commercial product was in iMovie 2, in which the buttons and the scroll bar acquired the Mac OS X Aqua look. It next proceeded to the Mac OS X Public Beta in autumn of 2000 before ending up in iTunes in January 2001.