Give an ACF Repeater subfield alternating classes, in this case, 'Odds' and 'Evens'. This can be applied to other things as well. Be creative. :)

acf_repeater_subfields_with_alternating_classes.txt

<?php if ( have_rows( 'acf_repeater_field' ) ) : ?>

	<?php $counter = 1 ; ?>

	<?php while ( have_rows( 'acf_repeater_field' ) ) : the_row(); ?>

	<?php
	if ( 0 === $counter % 2 ) {
		$class = 'even';
	} else {
		$class = 'odd';
	}
	?>

		<div class="<?php echo $class;?>">
			<?php the_sub_field( 'acf_repeater_subfield' );?>
		</div>

	<?php $counter++ ; ?>
	<?php endwhile; ?>

<?php endif; ?>