How To Speed Up Fade In / Out Process

I have an image menu that starts off as black and white and when the mouse hovers over it, it enlarges and changes to colour. It works a treat but I would like the transition from black & white to colour to be faster. Is there anyway of doing this without much(hardly any) flash knowledge.

Here is the fade in/out script:
MovieClip.prototype.fade = function(dir:String, addInteger:Number, f):Void {
delete this.onEnterFrame;
//this.step = (dir == "in") ? 0 : 100;
this.step = this._alpha;
this.onEnterFrame = function():Void {
this.step = (dir == "in") ? this.step+addInteger : this.step-addInteger;
this._alpha = this.step;
if (((dir == "in") && this._alpha>=100) || ((dir == "out") && this._alpha<=0)) {
delete this.onEnterFrame;
f();}};};