import flash.geom.*; //or more specifically ColorTransform

import fl.motion.Color;

var bgColorTransform:Color  = new Color();

bgColorTransform.setTint(galleryBackgroundColor , 1); //alpha is second parameter

bg_mc.transform.colorTransform = bgColorTransform;

————

Remove:

setTint(whatevercolour, 0); //dropping tint alpha returns object to original color

———–

Random Color:

var colorT:ColorTransform = new ColorTransform();

colorT.color = (Math.random() * 0xffffff);

addRect.colorSwatch_mc.transform.colorTransform = colorT;