SOURCE

let speed=3;
let d=50;
let x;
let y;
let c=0
function setup(){
   createCanvas(600,600);
   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);
   if(mouseIsPressed==true){
   x=mouseX+random(-speed,speed);
   y=mouseY+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>