----------------
BASIC CIRCA 1982
----------------
10  COLOR RND(15)
20  SET(RND(20),RND(20))  or something similar
30  GOTO 10

------------------
FLASH 7 CIRCA 2003
------------------

COLUMNS = 21;
ROWS = 21;
TILES_PER_PASS = 25;	// number of tiles to draw each pass
TILE_WIDTH = Stage.width/COLUMNS;
TILE_HEIGHT = Stage.width/ROWS;
counter = 0;
for (var i = 0; i<COLUMNS; ++i) 
{
	for (var j = 0; j<ROWS; ++j) 
	{
		var mc = this.createEmptyMovieClip("tile_"+counter, counter);
		mc._x = i * TILE_WIDTH;
		mc._y = j * TILE_HEIGHT;
		mc.beginFill(0);
		mc.moveTo(0, 0);
		mc.lineTo(0+TILE_WIDTH, 0);
		mc.lineTo(0+TILE_WIDTH, 0+TILE_HEIGHT);
		mc.lineTo(0, 0+TILE_HEIGHT);
		mc.lineTo(0, 0);
		mc.endFill();
		mc.itsColor = new Color(mc);
		counter++;
	}
}

this.onEnterFrame = function()
{
	for (var i = 0; i < TILES_PER_PASS; ++i) 
	{
		var r = random(ROWS*COLUMNS);
		var mc = this["tile_"+r];
		mc.itsColor.setRGB(  random(0x1000000)  );
	}
}

------------------
FLASH 8 CIRCA 2005
------------------

COLUMNS = 21;
ROWS = 21;
TILES_PER_PASS = 50;	// number of tiles to draw each pass
TILE_WIDTH = Stage.width/COLUMNS;
TILE_HEIGHT = Stage.width/ROWS;
import flash.display.BitmapData;
myBitmap = new BitmapData(COLUMNS,ROWS,false,0x000000);
this.createEmptyMovieClip('mc', 1);
mc.attachBitmap(myBitmap, 1);
mc._xscale = 100*TILE_WIDTH;
mc._yscale = 100*TILE_HEIGHT;
mc.onEnterFrame = function()
{
	for (var i = 0; i < TILES_PER_PASS; ++i) 
	{
		myBitmap.setPixel(random(COLUMNS),random(ROWS), random(0x1000000));
	}
}