let s = 0;

let b = 0;

​

function setup() {

  createCanvas(400, 400);

  colorMode(HSB);

  // HSB colour mode stands for hue, saturation, brightness

  // hue goes from 0 (red) - 360 (also red) 180 is cyan

  // saturation goes from 0 - 100 (black and white to colour)

  // brightness goes from 0 - 100 (black to white)

}

​

function draw() {

  background(h, s, b); //background colour is using

  h++; //the increment operator ++ increases the value of a variable by 1. 

  if( h >= 360){

   h = 0; 

  }

  // using mouse X,Y coordinates as the values for the S, B variables.

  s = map(mouseX, 0, width, 0, 100);

  b = map(mouseY, 0, height, 0, 100);

}