OK, it looks like compton is now in the repositories
so install it with:
then with the desktop effects disabled in the Peppermint Control Center, run this in a terminal:
DO NOT close that terminal or compton will exit .. but we'll get around to autostarting it at bootup if it works.
The above compton options give you dropshadows, but not under dock bars
You can see other compton options by running:
You could also try adding transparency of inactive windows with
but that really slowed down dragging windows around for me
Once you're sure you want t5o use it .. and know what the command is to get your ideal setup .. post that command here, and I'll tell you how to autostart compton with those settings.