In theme options, I had to define wp_editor_settings. So, just in options.php, I used:
//WP_editor settigs
$wp_editor_settings = array(
'wpautop' => true, // Default
'textarea_rows' => 15,
'tinymce' => array(
'plugins' => 'fullscreen,wordpress,wplink, textcolor'
));
Basically, I’m adding tinymce plugin.