Php Array list items with different class - php

Question

This is my current array that displays list items in a unordered list.
function get_bottle_colors() {
if(empty($_GET['cap_id'])) return false;
$constructor_img = get_post_meta($_GET['cap_id'], 'product_constructor_image', true);
if(is_array($constructor_img) && count($constructor_img)>0 && !empty($constructor_img[0]['title'])){
$output = '<label>Bottle Color</label><ul>';
foreach ($constructor_img as $key => $image) {
if(empty($image['image'])) continue;
$output .= '<li><a href="'.$image['image'].'" data-width="'.$img_size[0].'" data-height="'.$img_size[1].'"';
$output .= '</a></li>';
}
$output .= '</ul>';
}else{
$output = '<label>Bottle Color</label><ul></ul>';
}
echo $output;
die();
}
In total there will be up to 16 list items generated by this. I need each list item to have its own class eg: list class="red", list class="green", etc. Any idea how i go about achieving this?

Answer 1

Found the solution thanks to Anant. Had to declare the class array like below.
function get_bottle_colors() {
if(empty($_GET['cap_id'])) return false;
$constructor_img = get_post_meta($_GET['cap_id'], 'product_constructor_image', true);
if(is_array($constructor_img) && count($constructor_img)>0 && !empty($constructor_img[0]['title'])){
$output = '<label>Bottle Color</label><ul>';
$i = 0;
$class_array = array("a","b","c","d","e","f","g","h","i","j","k","l","n","m","n","o","p");
foreach ($constructor_img as $key => $image) {
if(empty($image['image'])) continue;
$category = 9;
$img_size = getimagesize($image['image']);
$output .= '<li class= "'.$class_array[$i].'"><a href="'.$image['image'].'" data-width="'.$img_size[0].'"
data-height="'.$img_size[1].'"';
$output .= 'data-id="'.$_GET['cap_id'].'_'.$key.'" data-part="#constructor-bottles" class="sub-caps">'.$image['title'];
$output .= '</a></li>';
$i++;
}
$output .= '</ul>';
}else{
$output = '
<label>Bottle Color</label><ul></ul>'; } echo $output; die(); }