In response to gardnerjohng's note to retrieve the first _key_ of an array:
To retrieve the first _key_ of an array you can use the combination of reset() and key().
<?php
$properties = array(
'colour' => 'grey',
'flavour' => 'rubber',
'name' => 'Mouse Ball',
'texture' => 'rubbery'
);
reset($properties);
echo key($properties); // => 'colour'
?>
I prefer this solution as you don't have to create the keys array. This should (not measured) improve performance on large arrays.