get key of array element php

1array_keys ($array);
2// It returns an array
3// more informations at https://www.php.net/manual/fr/function.array-keys.php (fr)

1$people = array(
2  2 => array(
3    'name' => 'John',
4    'fav_color' => 'green'
5  ),
6  5=> array(
7    'name' => 'Samuel',
8    'fav_color' => 'blue'
9  ));
10$found_key = array_search('blue', array_column($people, 'fav_color'));