What is the colors handle from WordPress core for and why does it not have a path?

Looping through $wp_styles->registered, the handle colors is outputted with a $wp_style->src of 1. Searching through WordPress core, it isn’t immediately clear what it’s for.

The code is:

 global $wp_styles;
    $wp_styles  = wp_styles();
    foreach ( $wp_styles->registered as $wp_style ) {
      echo $wp_style->handle . " | " . $wp_style->src . "<br>";
    }