float r = 100;
float g = 150;
float b = 200;
float a = 200;

float diam = 20;
float x =100;
float y = 100;

void setup () {
  size(500, 500);
  background(255);
}

void draw () {

  r = random(255);
  g = random(255);
  g = random(255);
  b = random(255);
  diam = random(20);
  x = random(width);
  y = random(height);

 noStroke();
 fill( r, g, b, a);
 ellipse(x, y, diam, diam);
}