var b= 255;

function setup() {

  createCanvas(600, 400);

}

​

function draw() {

  background(r, 0, b)

  r=map (mouseX, 0, 600, 0, 255);

  b=map (mouseX, 0, 600, 255, 0);

  fill(250, 118, 222);

  ellipse(mouseX, 200, 64, 64);

  //map has 5 arguments

  //line has 4 arguments

  stroke(250, 118, 222);

  line (200, 200, 100, 100);

}