Just following this discussion thread and I would agree with Richard’s choice of the tutorial link he added to his last comment.
The thing about Themes is that there are lots of things you can do and some of this is just alter the parts you need to use in order to do what you are asking to do.
In a former life when I was new to Moodle Themes I discovered that you can make some very basic child themes which are very simple in structure as they only carry with them the basics and leave the main structure with the parent theme.
So what I am trying to say is that all you would need is a style sheet for the main colour you want for each theme.
Parent theme name = moove
Child Theme Names = moove_red, moove_blue, moove_green, moove_yellow, etc.,
where these child themes would only need the basics...
In other words just a minimalist theme which is easy to maintain.
That said it is time consuming and not as easy as I have made it sound, but it is easier as you do not need to clone the parent theme totally, which is a mammoth task.
Hope this helps?