void setup()
{
  size(600, 600);
  background(220);

  colorMode(HSB);
}

void draw()
{
  float y, diam;

  y = 100;
  diam = 40;

  for (float x=diam/2.0; x<width; x+=diam) {
    fill(x%256, 255, 255);
    noStroke();
    ellipse(x, y, diam, diam);
  }
}