SOURCE

let x=50;
let d=50;
let y=50;
let a=40;
let b=50;
function setup(){
    colorMode(HSB,360,200,50);
    createCanvas(700,700);    
    noStroke(0);
}
function draw()
{let r=random(1,255);
print(r);
fill(r,100,100);
    //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://cdn.jsdelivr.net/npm/p5@1.1.9/lib/p5.min.js'></script>