Well, first of all you have to change ALL of your code that uses this cart structure -- not just this one sub -- if you want to switch the cart from a hash to an array. I actually think this is probably the wrong approach and you would be better off making unique item ids for every one of your colors. You could also cheat by making a generated key to use in your shopping cart: my $item_key = $item_id . '|' . $color or something like that.

Just to give you an idea of what you need to do to that code to change it to arrays, here is another take on your add_item sub:

sub add_item {
    my ($dbh, $cart_ref, $item_id, $qty, $color) = @_;
               
    # If the item isn't already in the cart, look it up from the datab
+ase
    # and store it in the cart as a new entry with a quantity of zero.
    my $saw_item = 0;
    foreach  my $item (@{$cart_ref}) {
        if (($item->{'id'} == $item_id) && $item->{'color'} eq $color)
+) {
            $saw_item = 1;
            break;
        }
    }
 
    if (!$saw_item) {
        my $sth = $dbh->prepare ("SELECT item_id, description, categor
+y, price, picture, thumbnail, mime_type, color FROM catalog_pet WHERE
+ item_id = ?");
        $sth->execute ($item_id);
        my $row = $sth->fetchrow_hashref ();
                                 
        return if !defined ($row);    # this shouldn't happen...
        my $item_ref = {};
        $item_ref->{description} = $row->{description};
        $item_ref->{price}       = $row->{price};
        $item_ref->{qty}         = 1;
        $item_ref->{color} = $color;
    }
    $item_ref->{qty} = $qty;
  
    push (@{$cart_ref}, @item_ref);
}
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Note that it is no longer possible to look up a single item in the cart by ID with this structure: you have to loop through all the items.