Using Anki 2.1.54, the editor does not apply CSS classes to editor fields. If I directly add a style=“color:red” attribute, it does change the color. But CSS classes make it far easier to change colors for every card at once. For example:
You don’t see the styling in the editor because the editor doesn’t show you a fully rendered version of your card. This means, in particular, that the card styling is never taken into account in the editor.
OK indeed that addon is broken in .54 but should be fixed in the next release. I’m still not clear whether it shows CSS class styles in the editor fields, but I can ask that on that addon’s thread.