function my_module_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'views_exposed_form') {
    // Exclude cases when query contains 'field_color_tid'.
    if (strpos($_SERVER['QUERY_STRING'],'field_color_tid') === FALSE) {
      // Act only if query string contains 'field_size_tid'
      if (strpos($_SERVER['QUERY_STRING'],'field_size_tid') !== FALSE) {
        $selected_tid = $form_state['view']->exposed_input['field_size_tid'];
        // Check if such taxonomy term exists.
        $term = taxonomy_term_load($selected_tid);
        if (!empty($term)) {
          // Redirect to taxonomy page.
          $path_alias = drupal_get_path_alias('taxonomy/term/'.$selected_tid);
          drupal_goto($path_alias);
        }
      }
    }
  }
}