This code is practically copied from the Coding Train tutorial. The link is here.
Toggle colour of a bubble
let bubbles = []; //create the bubbles function setup() { createCanvas(600, 400); for (let i = 0; i < 10; i++) { let x = random(width); let y = random(height); let r = random(20, 60); let b = new Bubble(x, y, r); bubbles.push(b); } } //click to remove the bubbles /*function mousePressed() { for (let i = bubbles.length - 1; i >= 0; i--) { if (bubbles[i].contains(mouseX, mouseY)) { bubbles.splice(i, 1); } } }*/ //if each bubble includes the cursor, change color, move & show anyways function draw() { background(0); for (let i = 0; i < bubbles.length; i++) { if (bubbles[i].contains(mouseX, mouseY)) { bubbles[i].changeColor(255); } else { bubbles[i].changeColor(0); } bubbles[i].move(); bubbles[i].show(); } } class Bubble { constructor(x, y, r) { this.x = x; this.y = y; this.r = r; this.brightness = 0; } changeColor(bright) { this.brightness = bright; } contains(px, py) { let d = dist(px, py, this.x, this.y); if (d < this.r) { return true; } else { return false; } } move() { this.x = this.x + random(-2, 2); this.y = this.y + random(-2, 2); } show() { stroke(255); strokeWeight(4); fill(this.brightness, 125); ellipse(this.x, this.y, this.r * 2); } }