code: function colorwheel(pos) {
    pos = 255 - pos;
    if (pos < 85) { return rgb2Int(255 - pos * 3, 0, pos * 3); }
    else if (pos < 170) { pos -= 85; return rgb2Int(0, pos * 3, 255 - pos * 3); }
    else { pos -= 170; return rgb2Int(pos * 3, 255 - pos * 3, 0); }
  }
docs: rainbow-colors, taken from http://goo.gl/Cs3H0v