size(200,200);
background (0);

for(int b=0;b<=200;b+=20){
  fill (0,255,0,b);
  noStroke ();
  rect (b,0,20,200);
}

ellipseMode(CENTER_DIAMETER);{
  for(int p=22;p<=200;p+=22){
    fill (0+p,0,200-p);
    ellipse (100,100,p,200-p);
  }
}

    Source: geocities.com/ar/laventanitainteractiva

               ( geocities.com/ar)