To do lists stay as they are. Doing lists turn red. Done lists are faded and greyed out.
If there's a todo or doing list on the board, all other lists are dimmed. List Highlighter works automatically with the title of your list, or with hashtags.
Just name your list Todo, Doing, or Done, and styles will be applied automatically. Or name it what you like and tag it with a hashtag (e.g. #todo, #doing, #done). The hashtag will only appear when you're editing the title.
For more information, see the List Highlighter homepage.