A HaXe method for applying a decimal (0 to 1) alpha to a 32bit ARGB hexadecimal colour, returning the recalculated 32bit ARGB hexadecimal value.

MergeAlpha.hx

/**
 * Merges a hexidecimal colour with a 0-1 alpha value and returns a new hexidecimal colour.
 * 
 * @param	Input ARGB colour that alpha will be applied to.  Eg: 0xFFFFFFFF (32bit ARGB).
 * @param	Alpha value will be applied to colour.  0 (fully transparent) to 1 (fully opaque).
 * @return Returns a new ARGB hexidecimal incorporating alpha.
 */
public static function mergeAlpha(colour:Int, alpha:Float):Int
{
	// Bitwise hex extraction.
	
	var a:Int = Std.int(colour >>> 24);
	var r:Int = Std.int(colour >>> 16 & 0xFF);
	var g:Int = Std.int(colour >>> 8 & 0xFF);
	var b:Int = Std.int(colour & 0xFF);
	
	return Std.int(a*alpha) << 24 | r << 16 | g << 8 | b;
}