I know this isn't the answer you're looking for, but if this panel is for your own use, my suggestion would be to pick the overlay with the colors you like best and use that one.
Aside from that, here's a scan of a Williams advertisment from 1982. (It's from the Williams Arcade Classics CD.) It's hard to tell from the poor quality of the scan which color scheme is pictured, but it might help. Also, I noticed a way to differentiate the two overlays regardless of monitor callibration - the top one in your picture has red lava flowing across the stone platforms, and the bottom one is lavaless.
One more suggestion - This is just a wild guess, but Williams released two versions of Joust. The first version allowed you to skewer pteradactyls forever. A second version was released which corrected this "bug." Maybe the two overlays you have pictured were used to differentiate the two versions of the game, in which case both could be considered "original colors." -Just a thought, I might be way off base here.
Regards,
Dave