SOURCE

let speed=20;
let d=50;
let x;
let y;
let c=0;
function setup(){
    createCanvas(480,480);
    x=width/2;
    y=height/2;
    colorMode(HSB,360,100,100,1);
}
function draw(){
    c+=0.1;
    if(c>360){
        c=0;
    }
    noStroke();
    fill(c,100,100,0.5);
    x+=random(-speed,speed);
    y+=random(-speed,speed);
    x=constrain(x,0,width);
    y=constrain(y,0,height);
    ellipse(x,y,d,d);
}

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