let xSpeed = 3;  // speed of ball

let color;

​

function setup() {

  createCanvas(400, 400); 

}

​

function draw() {

  background(250); 

  x+= xSpeed;

 //reverse

  if (x >= width || x <= 0) {

    xSpeed *= -1;

  }

color = map(x, 0, width, 255, 0);

  noStroke()

​

  fill(color);

​

  ellipse(x, height / 2, 100, 100);

}

​

​