Query all posts where a meta key does not exist

I am trying to get a query to retrieve all the posts where a specific meta_key does not exist and then create it.

I am having problems finding those posts as the query I am testing does not seem to work.

Here is the code I am using to try to get those posts:

$args = array(
   'posts_per_page' => 18,
   'meta_query' => array(
                     'key' => 'colors',
                     'compare' => 'NOT EXISTS'


This returns nothing if there are no posts with the key colors, but returns they ids of the posts with the key colors whenever that key is present (the opposite of what I need). I tried with EXIST instead but no luck.

If someone can tip me on the correct way of creating a query like the one I need I will appreciate it.


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