rgba-mixin that creates different code, depending on the envirnoment-variable "$isoldIE". If this variable is "true" only the filter for IE8 and before is printed. If the variable is "false" rgba-color is printed.

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);
  @if $isoldIE == false {
	  background-color: $color; // fallback for old browser that are not oldIE - very seldom
	  background-color: $rgba;
	} @else if $isoldIE == true {
	  background-color: transparent; // counteract against the defintion for older modern browsers
  	filter: progid:DXImageTransform.Microsoft.Gradient(GradientType=1, StartColorStr='#{$ie-color}', EndColorStr='#{$ie-color}');
	  zoom: 1; // trigger hasLayout		
	}
}