I never meant to imply that ALL the red ones where otherwise. There ARE read earth peas; the Nimyo picture proves that much. I merely meant that that particular specific seed in the photo looked to me more like a fat standard cowpea than an earth pea. There could have been several red seeds in that sample russ got, some earth peas, some not. You say that one of the plants looks more like a standard cowpea than an earth pea, maybe that was the one.
A 50-50 split sounds generous, but as I said, earth peas are not noted for their fecundity, so you could be looking at several to most plants only making one seed. My best advice would be to keep track of what colors each plant makes and plant to send 5 or so seeds from each one back. Maybe even send them with notes, so that they each can become a strain (so down the road, someone could say, "I want to grow the white seeded one with the black eye, the red one with the brown mottle, and the grey and silver ones (I didn't see a grey and silver one, but I believe that, as a species, Earth peas come in pretty much every color and pattern that cowpeas do, so somewhere out there should be silver ones, and mottle eyes, and blue ones. and so on)