13 lines, no comments · 139 tokens, written in 2 seconds for $0.0004

 1  function setup() {
 2    createCanvas(400, 400);
 3    noStroke();
 4  }
 5  
 6  function draw() {
 7    background(220);
 8    let r = map(mouseX, 0, width, 0, 255);
 9    let g = map(mouseY, 0, height, 0, 255);
10    let b = 150;
11    fill(r, g, b);
12    ellipse(mouseX, mouseY, 50, 50);
13  }