The earliest ones were clear, I think these were cast in acrylic. I've got a few in my collection that are tinted beautiful jeweltones. Then we started to cast in polyurethane, and the only color it came in was caramel, good thing it looked nice with the wood. I've seen cream, rust and a weird greenish color too.
I don't think these were special ordered at any time, just a reflection of the available materials.
By the mid 70's, the polyurethane finally came in black, and now they don't even make the caramel color anymore (but it comes in bunches of other colors). Our attempts to tint the white to a vintage caramel haven't made a satisfactory substitute for restorations.
Tony has made some really interesting pickups with the polyurethane colors. He's done some crazy splatters of red white and black and a rising sun starting with red then filling with white.