I'm afraid I have to take Russ and Marshall's side on that point, I love off types to death as well. While propagating a variety on is certainly a noble thing, to see a sport and know that you are one of the few people, if not the only person EVER in history to see that particular combination is something else entirely. It's almost a religious feeling; that the whims of nature have chosen you, and possibly you alone, to witness this new creation, and has entrusted you to use it correctly. It is a great burden, and a great honor.
Speaking a little less heavily. There are some cases I can remember from growing my own beans that make me aware the whole "strain versus landrace thing is often very complicated. I'm thinking mostly of last year, when I first grew the beans strains Bantu and Fort Portal Mixed (Neither is currently in Russ's list {though I swapped him some FPM this year, so eventually that one presumably will be} so you may not be familiar with either. Both of these were sold as landraces, and based on their appearaces I had no reason to question it. Both had a very wide range of colors. The Bantus looked a lot like the "Fort Portal Jade" bean Russ has (they're actually probably very closely related (see next parenthetical note) except instead of being bright green they vary between shades of brown, purple, olive and so on (all of these colors in fact are also occasionally produced by FPJ as well, which is why I ended up writing to Richter's as to whether I had gotten a mislabeled pouch, and they ended up fishing all the non-green ones out of their supply (what happened to those, I never found out) FPM had a similar color range (with some blacks thrown in) but is more of a kidney bean in shape.
Anyhow, I planted my seeds last year, and maybe 60% of them came up (a lot of the Richter's beans are now rather old, and as they don't regenerate stock, low germinations are pretty normal. Speckled Grey, which is one of the only two they still have any of in stock is currently at around 25% germination, and losing about 5-10% per year.) I lost a few plants over the year, but a decent number of the FPM made it to the end (in the case of the bantu nine plants made it as far as the first flush of pods, but eight immediately died afterward so my seed is rather skewed in favor of the one that kept on going)
Now here is the odd thing. Despite coming from many plants, with many seed colors, all plants produced IDENTICAL seed the next time around. Hot pink when fresh, bright purple when dry. The FPM produced a little variation, with seed being lighter or darker but this was between flushes, not plants (i.e. the seed from a given flush looked different from the seed from an earlier or later flush of the same plant, but the same as seed from the same flush from a different plant.) So I can only assume that, for these the seeds actually is of a single strain in each, and coat color is determined by some other factor (how hot is was when it matured, how fast it dried etc.)
And before anyone asks, no, I do not CURRENTLY have sufficient reserves of either bean to swap seed this year. Get back to me in another year when the season is more favorable and I have been able to increase my stock.