Forelle Fleiderfarben
I don't know why my beans come up in two separate tones like this; I always plant the purples but the beige ones seem to come up with the more purple ones. It's been like this since I first planted them.
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if you've been keeping track of your plants and checking seeds as they dry down you might notice how conditions may change the colors of the seed coats.
i've seen that myself where some seeds that finished earlier in cooler temperatures had different colors than those that ripened and dried down later when it was warmer and then again as the season came to an end. also the nutrients available in each location of each plant can change the color of the seed coat.
i think it is just a part of learning about each variety as you grow it through several years as to what it does and how it responds to the various conditions. some beans are more obviously reactive than others or more finicky.
some notables for me were Blaugrau, Bomba, Fort Portal Jade, Money, Nonna Agnes and recently with Tinker's Fire.
even the less finicky beans can still give some variations (Purple Dove is a good example in this regards as it has been very reliable and decently productive almost every place i grow it, but the seed coat color definitely changes depending upon where i plant it, the better the garden soil the better the color).
and i sure wished my Fukuruyu Chanaga beans had produced at all let alone such nice ones as those in your picture.

and Bantu is a wonderfully colorful mix. do they come true to color for each one planted or are you getting different colors from each seed planted? have you had to cull out ones that don't match or are you letting them give variations? i've found that almost everyy bean i grow for several years will give me things to cull out if i want to keep it true to what i started with.