Getting Keys from Select List

This is my first Drupal 8 site. I have a content type with a select list field. In my twig template I can print out the values. But I would like the keys too.

red_oak|Red Oak
white_oak|White Oak

I can get the values easy…

{{ content.field_colors }}

But what I want to do in my twig template requires access to that key..

<div class="red_oak">Red Oak</div>

This doesn’t work, but my initial thought was something like this…

      {% for key,value in content.field_colors %}
        Key : {{ key }}
        Value : {{ value }}
      {% endfor %}

Can anyone help me on this?

Drupal version: