Basically, I have no control over the myPort.read() values.
Sure you do. Turn the potentiometer. The values will change.
If that isn't happening, you need to investigate why not. Either the value from analogRead() is wrong because you wired the potentiometer incorrectly, or the values are right.
You can tell the difference by changing write() to println() and sending data to the Serial Monitor, instead.
If the values printed in Processing change as you turn the potentiometer, then the problem is in how you use the value in Processing. The comment says:
background(bgcolor, 255, 255); // hue, brightness, saturation. max value 255
This says that the potentiometer value is going to change the hue. I'm not sure exactly what that is supposed to mean. However, since you draw an image that might cover the whole background, I don't think you can expect to see changes unless the image has transparent areas of does not fill the frame.