Another rainbor generator, a little more complex

rainbow_2.js

function generateRainbowColors(count, createDiv, frequency1, frequency2, frequency3, phase1, phase2, phase3, center, width) {
  var colors = [];

  if(!count) count = 50;
  if(!createDiv) createDiv = false;
  if(!center) center = 128;
  if(!width) width = 127;

  if(!frequency1) frequency1 = .3;
  if(!frequency2) frequency2 = .3;
  if(!frequency3) frequency3 = .3;

  if(!phase1) phase1 = 0;
  if(!phase2) phase2 = 2;
  if(!phase3) phase3 = 4;

  var ww = window.innerWidth;
  var w = Math.ceil(ww / 30);
  var x = 0;
  var y = 0;
  
  function byte2Hex(n) {
    var nybHexString = "0123456789ABCDEF";
    return String(nybHexString.substr((n >> 4) & 0x0F,1)) + nybHexString.substr(n & 0x0F,1);
  }

  function RGB2Color(r,g,b) {
    return '#' + byte2Hex(r) + byte2Hex(g) + byte2Hex(b);
  }

  var red, green, blue, color;

  for (var i = 0; i < count; i++){
    red   = Math.sin(frequency1 * i + phase1) * width + center;
    green = Math.sin(frequency2 * i + phase2) * width + center;
    blue  = Math.sin(frequency3 * i + phase3) * width + center;

    color = RGB2Color(red, green, blue);
    colors.push(color);

    if(createDiv) {
      var div = document.createElement("div");
      div.style.position = "absolute";
      div.style.left = x + "px";
      div.style.top = y + "px";
      div.style.width = w + "px";
      div.style.height = w + "px";
      div.style.backgroundColor = color;

      document.body.appendChild(div);

      x = x + w;
      if(x > ww){
        x = 0;
        y = y + w;

        div.style.left = x + "px";
        div.style.top = y + "px";
      }
    }
  }

  return colors;
}