rainbow7.js

var hue;
var rainbow = true;

function setup() {
  createCanvas(windowWidth, windowHeight);
  background(0);
  hue = 0;
}

function draw() {
  // background(220);
}

function mouseDragged() {
  if (rainbow) {
    if (hue > 360) {
        hue = 0;
    } else {
        hue++;
    }
	}
  colorMode(HSL, 360);
  noStroke();
  fill(hue, 200, 200);
  ellipse(mouseX, mouseY, 25, 25);
}

function keyPressed() {
  if (keyCode == 82) {
    hue = 0;
    rainbow = false;
  }
}