Thanks for the reply Jeffery. So a new Trim Package is the old way to change the Trim (except the Paintbrush)
I did use the Paintbrush, which is tedioud) and it changes the Trim, but I then saw what you mean about the Trim not wrapping around the openings. After painting the trim and then the wall edge, I ended up with a narrow strip of white around the window, so I zoomed in close to Paint it and the whole wall became my timber colour!
Now I don’t know how to change that strip of wall colour inside the window opening! Presumably the Trim package does not include a frame inside the opening. Surely it must? Or is the inner frame not wide enough, leaving a bit of wall showing?