function toColorHexString(ref) {
  var results = [];

  var _iterator = _createForOfIteratorHelper(ref),
      _step;

  try {
    for (_iterator.s(); !(_step = _iterator.n()).done;) {
      var r = _step.value;
      results.push(toHexString(r));
    }
  } catch (err) {
    _iterator.e(err);
  } finally {
    _iterator.f();
  }

  return '#' + results.join('');
}
Converts from an array of numbers like [15, 15, 15] to a hex string like 'FFF'
@param {[red, green, blue]} ref
@returns {string}