dxb, since each stand of silk fiber is about half to one fourth the thinkness of a strand of hair, sink is rarely make from a single strand, but is made from 2 to 20 or so strands spun together.

i know slubbed silk (i had, as a teen, a 'shell'-a simple sleeveless top made from a scrap of slubbed silk) but it didn't not have the shimmer effect you spoke of. I would guess it either is double strand is dyed different colors, and then the 4 (2 sets of double) strand are then spun, or
the different colors also could have been warp and weft of the woven fabric, but the slubs in the silk i had were all horizonatal, non were verticle. but it did have the crisp, but still drapable hand that is described.

Habutexiles http://habutextiles.com is the most recent site i have found about spinning/weaving silk, and i didn't see anything there about duponi silk. (nor have i ever heard of it.)