Remove last comma from array

Hello,

How can I not show the last comma in an array.
I have the following code:

<?php
$values = get_field('systeem');
if($values)
{
	echo '<li>Color(s) used: <span class="white">';
	foreach($values as $value)
	{
		echo $value . ', ';
	}
	echo '</span></li>';
}
; ?>

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