Add drop down list filter to search action

The following actions in a controller get the search person page and return the search person results.  At the moment, I have one drop down list filter for the country of birth, one drop down list filter for city and two other search filters by “age” and “gender”. I want to add an additional drop down list filter which will allow me to search by hair colour. I am a little bit inexperienced in this area and need some help to be able to do this. 

  /// <summary>
  /// Gets the person search page.
  /// </summary>
  /// <returns>
  /// The person search page.
  /// </returns>
  /// GET: /Person/Search
  [HttpGet]
  public ActionResult Search()
  {
  return
  this.View(
  new PersonSearchViewModel
  {
CountryViewModel =
  new CountryViewModel
  {
Country =
  new SelectList(this.countryManager.GetCountries(), “Name”),
 Cities = new SelectList(new List<City>(), “Name”)
  }
  });
  }

  /// <summary>
  /// Searches the person.
  /// </summary>
  /// <param name=”viewModel”>
  /// The <see cref=”PersonSearchViewModel”/> to filter by.
  /// </param>
  /// <returns>
  /// The <see cref=”ActionResult”/>.
  /// </returns>
  /// POST: /Person/Search
  [HttpPost]
  public ActionResult Search(PersonSearchViewModel viewModel)
  {
  viewModel.CountryViewModel = new CountryViewModel
  {
 Countries = new SelectList(this.countryManager.GetPCountries(), “Id”, “Name”),
 Cities =
  viewModel.SearchCriteria.CountryId > 0
  ? new SelectList(
  this.countryManager.GetCitiesviewModel.SearchCriteria.CountryId.GetValueOrDefault()),
  “Id”,
  “Name”)
  : new SelectList(new List<City>(), “Id”, “Name”)
  };

  viewModel.PersonViewModel = new PersonViewModel
  {
  People = new SelectList(this.personManager.GetAllPeople)),
  };

  if (!this.ModelState.IsValid)
  {
  return this.View(viewModel);
  }

  viewModel.SearchResult = this.peopleManager.FindPeople(viewModel.SearchCriteria, 1234);

  return this.View(viewModel);

  }