I won’t take up much of anyone’s time with this, but I’m so happy I just had to share it. My transparency problem is solved! Yay!
As it turns out, this was an issue I would have never, ever figured out on my own. Nothing I was doing “wrong,” just a quirk deep within the Maxis coding that didn’t show up until the notorious “Pets” expansion pack and isn’t addressed in ANY of the tutorials.
Have a look: