Hi,
What you would need to do would be something along the lines of:
<?php if(get_field('color')) {
$color = get_field('color'); ?>
<div class="title-item" style="background-color:<?php echo $color ?>;">
<?php } else { ?>
<div class="title-item">
<?php } ?>
<h4><?php the_title(); ?></h4>
</div>
