OK first off let me say EW.
This cape was made over the course of four years, from the silk of over a MILLION Madagascar Golden Orb spiders. So naturally my first thought is, "OMG there are over a million golden orb spiders, help!" So I'm just hoping it wasn't a million separate spiders, and maybe more like five or six they just caught repeatedly several thousand times. Anyway, the silk was gathered each day by hand, and its yellow color is naturally occurring.