This will change the colour of a clip to random values between #000000 and #ffffff every second (converted to base 10 rather than hex so it's easier to generate the random number), all you need is a clip on the stage with instance name 'myClip'...
function doRandomColour(clip) {
myColor = new Color(clip);
var colourCode = Math.round(Math.random()*16777216);
myColor.setRGB(colourCode);
}
//
setInterval(doRandomColour, 1000, myClip);
//
stop();