float a = random(0,255);
float b = random(0,255);
float c = random(0,255);
int circle_color=color(a,b,c);
int i;

void setup() {
  size(800,800);
  background(255);
  strokeWeight(2);
  frameRate(25);
}

void draw() {
  background(0);
  stroke(255);
  fill(circle_color);
  ellipse (400,400,mouseX,mouseY);
  for(i = 0; i < 39; i = i+3){
    fill(circle_color);
    ellipse (400,400,mouseX-(20*i), mouseY-(20*i));
  }
  a = random(0,255);
  b = random(0,255);
  c = random(0,255);
  circle_color = color(b,c,a); 
}