function setup() {

  // createCanvas(width, height)

  createCanvas(600, 400);

  noStroke();

  background(220);

}

​

function draw() {

  let brushDiameter = dist(mouseX, mouseY, pmouseX, pmouseY);

  if(mouseIsPressed == true){

    noStroke();

    fill(mouseX, 0, 200, 128); // fill(red, green, blue, alpha) 0 - 255

    circle(mouseX, mouseY, brushDiameter); // circle(x, y, diameter)

  }else{

    noFill();

    stroke("white");

    circle(mouseX, mouseY, brushDiameter);

  }

}