Creating ellipses with different colours and sizes

Processing Beginners
9

i think the question is about REDRAWING

so when you try

float radius = 200.0;

void setup () {
  size(500, 500);
  background(100, 100, 255);
}

void draw () {
  noStroke();
  //background(100, 100, 255);
  fill(255, int(random(255.0)), 0);
  radius = random(200.0);
  ellipse(width/2, height/2, radius, radius);
  delay(100);
}

it might be close to what you want,
but now you try to enable line 10 again ( by removing the // )
and you see that the background(); in the draw loop
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