Silk taffeta seems very plausible as it did have the kind of luster that silk would provide. I didn't find anything on the web that showed how it's made but I can imagine that if one were to weave two colors - one color as the warp and one as the weft - you might get the effect that I saw. Somehow I don't think that a silk taffeta kilt would be very practical.

Surely it was not just a purplish fabric that looked different at different places on the stage. The colors would shift if the actress remained in place but merely turned to face a different direction.