Drupal 7 Themeing - template.tpl.php vs template.php - variables

Question

I am interested in learning what disadvantage, if any, there are in calling variable fields directly within the template.tpl.php files.

Is it ok to place a field variable within the template.tpl.php file if doing it as simply as:

<?php 
//--------------------------------
// COLOR
if(!empty($content['product:title']['#product']->field_taxonomy_color['und'][0]['taxonomy_term']->name)): ?>
    <div id="color-wrapper">
    <?php
        $max_length = count($content['product:title']['#product']->field_taxonomy_color['und'])-1;
        for($x = 0; $x <= $max_length; $x++){
            echo '<div class="color">'. $content['product:title']['#product']->field_taxonomy_color['und'][$x]['taxonomy_term']->name .'</div>';
        }  
    ?>
    </div>
<?php endif; ?>

My understanding is that this code should be placed a preprocess function and called into the tpl.php file such as:

TEMPLATE.PHP

function theme_preprocess_node(&$variables) { $variables['color'] = ... }

TEMPLATE.TPL.PHP

<?php echo $color; ?>

If this is the case, how would i return all values of the loop from template.php into template.tpl.php?

---------EDIT---------
Should I create complex logic within its own field--template.tpl.php file, set the field to a variable in template.php and call upon the variable inside the node--template.tpl.php? Would there be a problem with creating over a hundred field--template.tpl.php files?

Answer 1

The disadvantage is you leak a lot of PHP code processing Drupal inner structures to the template file.

I would preprocess $content in template.php to expose a simple array of strings as a custom variable:

$colors = $content['product:title']['#product']->field_taxonomy_color['und'];
$colorNames = Array();
for ($x = 0; $x < count($max_length); $x++) {
  $colorNames[$x] = $colors[$x]['taxonomy_term']->name;
}
$variables['color_names'] = $colorNames;

Then the template code could be:

<?php if ($color_names): ?>
<div id="color-wrapper">
  <?php foreach ($color_names as $cn)
    print '<div class="color">' . $cn  . '</div>'; ?>
</div>
<?php endif; ?>