In 1996, I lived walking distance from Mike Fuller, and remember all his early pedals. He had a couple guys and him assembling them in his small guest house.
The silver FD2's were essentially prototypes that he made his name on, to launch Fulltone. They didn't make many, so yours could be considered collectible.
As soon as Guitar Center wanted to sell his pedals, he came up with his signature enclosures, and the FDII came out in orange with no mini switches or pullup knobs.
A few months later, he added a pullup volume for flat mids. A year later, the color changed to blue w/pullup, then mini switches. In following years, they made various tweaked versions as Fulltone grew bigger and changed locations.....yellow, cream, candy apple 10th Ann, black FDIII. The Fulldrive II has quite a legacy.
I've had the early orange, blue, and cream. I've owned many Fulltone pedals over the years. The only one I still have is the Choralflange.