Sequential colors

here is a script that allows a random color to be displayed, how do I alter the script to make it not random but, sequential from white through all the colors to black. Here is the script:

onEnterFrame = function () {
myCol = Math.round(Math.random()*Math.pow(6, 16));
beginFill(myCol, 50);
moveTo(100, 100);
lineTo(200, 100);
lineTo(200, 200);
lineTo(100, 200);
lineTo(100, 100);
endFill();
};

cheers,

norm125