function setup() {

  createCanvas(600, 400);

  background(190);

  noStroke();

}

​

function draw() {

  // background(220);

  if(mouseIsPressed == true){

    noFill();

    stroke(200, 0, 200, 80);

  }else{

    // fill is taking red, green, blue, opacity

    // from 0 to 255 where 255 is max 

    fill(200, 0, 200, 80);

  }

  diameter = dist(mouseX, mouseY, pmouseX, pmouseY);

  circle(mouseX, mouseY, diameter);

}

​

function keyPressed(){

  print(key);

  if(key == ' '){

    background(190);

  }

}