Oh interesting. Also, how do you know this?! I feel like I've come across this treasure trove of bean knowledge here -- like really deep stuff, history and culture and whatnot.
I put Fort Portal into the internet, and got both a geographic and altitude map.
Curious that you got so much variation in your beans. I'm pretty sure some of the colours I planted from Bantu didn't come up, while a boring wrinkly gray one that I don't remember planting was quite abundant. I got some mustard ones too, but I wasn't quite sure if it was from a neighbouring bean. There was a very fun lemon-yellow one too!
Well, someone else who planted out Bantu got a odd mottled skinned bean in their growback (odd in that, like your grey one, it isn't the same shape as the rest.)
As for the Mottled Grey variations (which are really the only ones, as I mentioned the Fort Portal Mixed all came back as one as well) since beans tend to mostly self pollinate, having things come back more or less as they were is pretty much the NORMAL outcome. Joe Simcox probably saw a mix of Fort Portals and the Pebblestone like beans, thought it was all one variable type and offered it as such (a lot of the seed he offers IS the actual seed he collects, no middle grower, so it IS possible.) The other colors are probably just a few odd ones that fell in the pile and went along for the ride.
I think something sort of similar happened in the creation of Owl's Eye (one of my cowpeas) When I got the original mixed bean bags I found them in from the supermarket, there were basically three types, one that was white with a brown eye, one that was mottled all over, and one with a mottled eye (which was the commonest, and what became Owl's eye.) Probably the first two were the original types, and the third was the result of a cross (which then got selected over them). There was also a few red and white yin yang ones, but those again were probably outliers.
And Speckled Eye (another cow pea, and one I can theoretically still get, unlike Owl's) probably has a similar story based on how I find it, a brown eyed pea, a speckled all over pea, and a speckled eye pea.
And there is actually a "lost color" in the Bantu/Fort Portal Jade group. I already mentioned that I found a purple seed in my Fort Portal Jade (and that got planted with, and possibly incorporated into, the Bantu population.) What I DIDN'T mention was that there was also a steel blue one. But I lost that seed before I could plant it.
). I planted borage in the middle of the larger garden last year, and it acted like a bee magnet! The bumbles were still bobbing along through the garden, doing their thing, but otherwise the winter squash was ignored. Which was pretty much the opposite of what I was aiming for! 
Are they good as dry beans?
what i want to do is export all the e-mails into a different format and of course there is no easy way to do that as of yet. i'll keep looking.
lol
