Test: P5.js

function setup() {
  createCanvas(255, 255);
  noStroke(); fill(0);
  textSize(16);
  text('TEGN!',0,16);
}

function draw() {
  var x = mouseX;
  var y = mouseY;
  fill(x,y,random(0,255));
  ellipse(x,y,10,10);
}