how to set $chart['#data_colors'] using chart_unique_color();

I have a bar chart and wanto use chart_unique_color to get some unique color, but i found an problem to put array value to $chart['#data_colors'] .

my code is

<?php
	while ($my_row = db_fetch_array($result)){
		$year_val[] 			= $my_row['year_val'];
		$month_val[] 			= $my_row['month_val'];
		$year_month_val[] 		= $my_row['year_val'] .'-'. $my_row['month_val'];
		$count_of_task[] 		= $my_row['count_of_task'];
		$legend[] 			= $my_row['year_val'].'-'.$my_row['month_val'] .' '. $my_row['count_of_task'];
		$data_colors[] 		= chart_unique_color($my_row['month_val']);
	}


	  $chart['#data'] 		= $count_of_task;
	  $chart['#legends'] 	= $legend;
	  $chart['#data_colors']= $data_colors;

	  //------------------- cek $data_colors array --------------------
	  $array_data_colors = print_r($chart['#data_colors'], true);
	  drupal_set_message('$array_data_colors = ' . $array_data_colors);
	  //------------------- cek $data_colors array --------------------
	  
?>

I have print $chart['#data_colors'] to cek, but still have problem, my bar only displayed one color as figure in attached file.

Pls help me.