Converts a solid color with an alpha-channel-value into rgba and an IE-filter as fallback for oldIE (IE up to version 8).

all-rgba.scss

// Converts a solid color with an alpha-channel-value into rgba 
// and an IE-filter as fallback for oldIE (IE up to version 8)
@mixin all-rgba($color, $alpha) {
    $rgba: rgba($color, $alpha);
    $ie-color: ie-hex-str($rgba);
  background-color: $color;
	background-color: $rgba;
    /* for oldIE */
	*background-color: transparent;
  	filter: progid:DXImageTransform.Microsoft.Gradient(GradientType=1, StartColorStr='#{$ie-color}', EndColorStr='#{$ie-color}');
	zoom: 1;
}

call-the-mixin.scss

.test {
    @include all-rgba(rgb(162,0,0),0.2);  
}

result.css

.test {
  background-color: #a20000;
  background-color: rgba(162, 0, 0, 0.2);
  /* for oldIE */
  *background-color: transparent;
  filter: progid:DXImageTransform.Microsoft.Gradient(GradientType=1, StartColorStr='#33A20000', EndColorStr='#33A20000');
  zoom: 1;
}