SOURCE

let x=30;
let d=50;
let y=50;
let a=28;
let b=18;
function setup(){
    colorMode(HSB,360,150,100);
    createCanvas(500,500);
    noStroke(0);
}
function draw()
{let r=random(1,250);
print(r);
fill(r,90,90);
    //background(120);
    x+=a;
  if((x>550)||(x<0)){
        a=-a
    }  
    y+=b;
    if((y>550)||(y<0)){
        b=-b
    }
    ellipse(x,y,d,d);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script>