Wow, first webdev post in like, forever, must be because I mocked up a first draft of the new portfolio page.
CSS3 introduces the rgb and rgba background properties. Simply put, instead of hexes, colors can be determined by their rgb values.
This is background:rgb(0,0,0); , which is black.
That’s nothing special. rgba, however, combines background color and alpha value, or opacity.
This is background:rbga(0,0,0,.6); , which is black and 60% opacity.
Please note that rgba only specify a specific element, whereas opacity property define an element and its children. The latest Firefox and Webkit browsers support this, IE8 and below… not so much. It only supports rgb.
CSS Tricks has a whole list of browser support. This is a handy property that replaces the 1px translucent background image.