The idea of the instant coffee mixed in with the superglue as a tint is intriguing and now I wish I had known/thought of that before I did the Philco to see how it works as that set has a very plain brown finish and is not mottled at all so it would have worked great if it does tint the glue.
I have used brown microballons/cyanoacrylate as a filler material for bakelite, too. One thing I haven't seen done here is to use the CA glue *as* a finish. Squirt some on, and rub it briskly with a wadded-up paper towel until it gasses off. DON'T STOP rubbing briskly until it is good and set, you can guess why. It's pretty shiny in the middle of the rubbed area, and a little rough at the edges. Build up enough and you can then use it like a sandable glaze, or to replace the shiny surface glaze/crust if you have had to sand through it. You end up with a rock-hard clear acrylic surface. The cheapest hobby shop "thin" or "instant-cure" works well and it doesn't take very much at all to do a radio.