theme-settings.php

<?php

/**
 * USAGE:
 * 1 - To use this file replace "adaptivetheme_devtheme" with the name of
 *     your theme in the function below.
 * 2 - Set 'style_enable_schemes' to 'on' in your themes info file (its near the bottom of that file).
 * 2 - Build or un-comment the forms. The Style Schemes form is ready to use,
 *     just un-comment it.
 */

// Replace 'adaptivetheme_devtheme' with your themes name, eg:
// function your_themes_name_form_system_theme_settings_alter(&$form, &$form_state)
function adaptivetheme_devtheme_form_system_theme_settings_alter(&$form, &$form_state)  {

  // Style Schemes
  /* -- Delete this line if you want to use Style Schemes

  if (theme_get_setting('style_enable_schemes') == 'on') {
    $form['style'] = array(
      '#type' => 'fieldset',
      '#title' => t('Style settings'),
      '#collapsible' => TRUE,
      '#collapsed' => TRUE,
      '#weight' => 90,
      '#description'   => t('Use these settings to modify the style of your theme, such as the color scheme.'),
    );
    $form['style']['style_schemes'] = array(
      '#type' => 'select',
      '#title' => t('Styles'),
      '#default_value' => theme_get_setting('style_schemes'),
      '#options' => array(
        'none' => t('None'),
        'style-default.css' => t('Default Style'),
        // 'my-style.css' => t('My Style'), // Add your schemes, these MUST be placed in your subthemes /schemes directory!
      ),
    );
    $form['style']['style_enable_schemes'] = array(
      '#type' => 'hidden',
      '#value' => theme_get_setting('style_enable_schemes'),
    );
  }

  // */
}