Calculating RBG-color

This is not a AS3-specific question, but I will place it here anyway… :hitman:
So I got a color, let’s say [COLOR=#ff0000]**0xFF0000 (red)
**[/COLOR]And I got another color, **black **with [COLOR=#808080]50% transparency[/COLOR].

What I got at the moment is these two colors combined in 2 different sprites that
obviously makes some [COLOR=#b22222]wine-red[/COLOR] color.

I was thinking of a smart way to combine these colors without making 2 sprites,
so I do like this: *0xFF0000 + (my 50% black color) = the color I want,
*but unfortunately I couldn’t come up with something…

If anyone understand my problem and can point me into the right direction,
it would be very appreciated!

~Tompa