After sifting through a tiny fraction of the weld seeds I had collected and dried, I began to wonder whether I actually needed to separate them by color. More accurately, I began to hope that I didn’t have to, because even with the double-sift/shake-down method, progress was slow.
I decided to do a germination test. On July 3rd, I planted some yellow seeds, some brown, and some black. Lo and behold, a month later, none of the yellow or brown seeds had germinated, only the black ones had. These photos are from August 2nd.
Granted, it was a small-scale trial (I only filled 6 cells with each type of seed), but still I felt pretty satisfied that the lightest colored seeds are, in fact, immature, and not worth saving.