>>9683643I believe these old raised baseplates were colored via something called aqueous printing.
Basically, there is a thin layer of paint / print on top of water, and then the item is dipped into it to apply. You can see this done with high end things like helmets or car parts.
Basically, this was dipped upside down.
Thanks for the heads up. I am a collector and will be bidding on this, I have at least one of every raised baseplate. For example, picrel is oddly rare and I didn't know it existed for a good while.