Welcome to the forum tittom.
I've just checked your work-flow with 1.4.6 on Windows using the Cleanlooks theme - Windows doesn't have an Aqua theme - and it works fine for me (see attached).
I can't check on OS X at the moment but I can't remember seeing that problem in all the years I used it on my old Mac, although I might not have noticed it.
Does the text actually change colour - only visible after the text has been de-selected - even if the drop-down list says otherwise, or does the text always stay the same? How does your experience differ from that in my attached "video"?
There are some differences between the different OS versions of Scribus so this might be another one.
Note: You shouldn't have to press PF2 to get the Properties Palette open unless you have closed it. Just keep it open all the time and it will automatically change according to what it selected. (This is something that is very important but isn't made clear in the documentation. The official tutorial, as it currently reads, seems to infer that you need to open it each time which gives the wrong impression.)
Edit: I have just changed the tutorial -
https://wiki.scribus.net/canvas/Get_Started_With_Scribus:4#Soul_of_Scribus - to tell people to always have the PP open. Hopefully this will prevent misinterpretation in the future. (Editors of other Scribus documentation should also make this clear to their readers.)