Вот примерчик

Код:
//ширина и высота мувиклипа, кол-во кадров анимации
var MC_WIDTH:Number = 200;
var MC_HEIGHT:Number = 200;
var FRAMES_TO_ANI:Number = 10;
//---
var frame_counter:Number = 0;
var color:Number = 0xFF0000;
var r:Number = 0;
var g:Number = 0;
var b:Number = 0;
_root.createEmptyMovieClip("animate_mc", _root.getNextHighestDepth());
_root.animate_mc.onEnterFrame = function()
{
if (frame_counter < FRAMES_TO_ANI)
{
this.beginFill(color, 100);
this.moveTo(0, 0);
this.lineTo(MC_WIDTH, 0);
this.lineTo(MC_WIDTH, MC_HEIGHT);
this.lineTo(0, MC_HEIGHT);
this.lineTo(0, 0);
this.endFill();
r = ((color) & (0xFF<<16));
g = ((color) & (0xFF<<8));
b = ((color) & (0xFF));
r -= (Math.floor(255 / FRAMES_TO_ANI)<<16);
b += (Math.floor(255 / FRAMES_TO_ANI));
color = r + g + b;
frame_counter++;
}
else delete this.onEnterFrame;
}