How to output a custom field in my template?
This is a perfect use case for the Field Formatter CSS Class module.

After adding a text list, radio, or taxonomy field to a content type, you then put the field on the view mode you would like for the class to be on. Use the CSS Class formatter and what level you would like to apply the class (generally node is fine), then you can add your CSS rules for whatever you want.

For example, you can change the individual caption background color on slides in a rotator, or specific stylings per post in a blog feed.