Function for alpha blending

gistfile1.sass

// Turns out this function already exists in Sass: mix(fg, bg, %) (http://d.pr/mGqa)

// Alpha blending

@function blend($bg, $fg) {

	$r:   red($fg) * alpha($fg) +   red($bg) * (1 - alpha($fg));
	$g: green($fg) * alpha($fg) + green($bg) * (1 - alpha($fg));
	$b:  blue($fg) * alpha($fg) +  blue($bg) * (1 - alpha($fg));

	@return rgb($r, $g, $b);

}