The Mac OS X 10.0-10.4 'lickable' interface: pinstriped windows, candy-gel capsule buttons with a wet top highlight, brushed-metal panels, traffic-light window controls, and the pulsing blue default button. Everything glossy is a capsule; everything structural is soft gray; light always enters from directly above.
Primary actionThe gel button: a pill with a saturated blue base, an inset white top highlight covering the upper half like a bead of water, a soft under-glow at the bottom edge, and — for the default action — a slow opacity pulse.