on, no, they were definitely using Jell-O (tm) brand vegetable flavored gelatin! There were a whole bunch of savory flavors in the 40s and 50s.

I've thought about trying to make my own using unflavored, but I've never seen Jell-O brand unflavored and it always feels like the knox sets differently, so idk about trying it with a new recipe. I'll probably just use lemon, which was mentioned as an option for some of them.