LESS CSS preprocessor: Is there a way to map a single color to an rgb and rgba definition?

Question

I'm trying to write a block in the CSS preprocessor LESS that will do the following:

@transparent_background(@color; @alpha: .8)
{
  background: @color;
  background: rgba(<color R value>, <color G value>, <color B value>, @alpha);
}

Is there any way to get the RGB values out of @color if it's a standard hex definition (i.e. #rrggbb)? Is there a way to do this if @color is defined some other way?

EDIT: SOLUTION

@transparent_background(@color; @alpha: .8)
{
  background: @color;
  background: @color + rgba(0, 0, 0, @alpha);
}

Answer 1

Try this:

background: @color - rgba(0, 0, 0, 1.0) + rgba(0, 0, 0, @alpha);

The subtraction will clear the alpha channel on @color then you just add the desired @alpha to the alpha channel. Colors have the full suite of operators and they work component by component when operating on two colors; colors are stored as RGBA components internally so this should work. Also, the alpha channel is normalized to be in the interval [0, 1.0] so subtracting 1.0 from the alpha channel should clear it without causing any problems.

I don't have CSS LESS set up right now so I can't check but this is worth a shot.

Answer 2

None of the solutions work anymore, but this one does (thanks to @Elyse):

.alpha(@color, @alpha: 0.8) {
    color: @color;
    color: hsla(hue(@color), saturation(@color), lightness(@color), @alpha);
}

The hsla() function, while not advertised in the LESS website, is defined in the source code.