// initializing variables
int interval; // how often changes

void setup() {
  size(300,300);
  smooth();
  noStroke();


} // end setup


void draw() {
  background(255);

  if (interval % 100 == 0)  {
    background(255,0,0);
    }

  interval = interval+ 1; // count each loop!
  println("interval: "+interval);
} // end draw