Why does jQuery .css('background-color') return rgba(0,0,0,0) for 'transparent'?

I have a box here - http://jsfiddle.net/U68p3/2/ - with a transparent background. When I read the background with jQuery's .css('background-color') it returns

               rgba(0, 0, 0, 0) 

which is not very helpful if my code is looking for a match with 'transparent'.

Why is jQuery doing this and is there a way I can make it return 'transparent'?

Thanks.

$(function() {
    var bkgnd = $('#box').css('background-color');
    console.log('background-color is ' + bkgnd);
});