There are theme settings for both Plain Text and Code and Rich Text. Settings in the Plain Text and Code menu do not affect Rich Text nodes. If you’re trying to change the theme for Rich Text nodes you should select a different theme in the Rich Text preferences menu.
As a matter of fact yes. That was exactly what I was missing apparently.
And I found I can change background and text colours for rich text without
needing to restart the app. Easy when you know it, and thanks for the help
It seems confusing though with separate theme settings per type of content.