Generate different colors Google Chart

I am having doubts about how to generate the colors directly in the config when executing the code and where to add the colors to be generated, if in this case I should generate another graphical array? array('colors' => $obj->color) or should I add another while to the config?

  $grafico['config'][] = array('c' => array(
  array('v' => $obj->color),

    array('v' => (int)$obj->total)
));



  // Estrutura basica do grafico
  $grafico = array(
'dados' => array(
    'cols' => array(
        array('type' => 'string', 'label' => 'dados'),
        array('type' => 'number', 'label' => 'Total')
    ),  
    'rows' => array()
),
'config' => array(
    //'pieSliceText'=> 'label',
    'is3D'  => 'true',
    'colors' => '', // Aqui as cores vindas da database
    'title'  => 'Quantidade de eventos',
    'width'  => 800,
    'height' => 300

  )
);

// Consultar dados no BD
  $pdo = new PDO('mysql:host=localhost;dbname=ccs',   'cc', 'xxx);
  $sql = 'SELECT category.*,(SELECT COUNT(*) FROM event WHERE category_id =      category.id) as total FROM category';
  $stmt = $pdo->query($sql);
  while ($obj = $stmt->fetchObject()) {
  $grafico['dados']['rows'][] = array('c' => array(
    array('v' => $obj->name),

        array('v' => (int)$obj->total)
  ));

}


// Enviar dados na forma de JSON
header('Content-Type: application/json; charset=UTF-8');
echo json_encode($grafico);
 exit(0);