Problems dynamically assigning value for setRGB

I was after a way to make a clip transition through a number of shades/colors by assigning a color objects “setRGB” method to a number which decreases every frame.

[AS] stop();
next_color=new Color(“useit”);
var num=0;
useit.onEnterFrame=function(){
num+=1;
next_color.setRGB(num);
trace(num);
} [/AS]

Everything sought of starts off promising, but then the colors seem to get stuck in some kind of loop & revert back to the colour set at authoring before transitioning again.

Anyone any idea what is going on here or why it won’t work?

Fla attached