I have used rayon since 1992 when I bought my first embroidery machine and embroidered towels I still use. The colours are fine after years of laundering. But then there's no bleach in washing powders / liquids in my part of the world and I never use bleach for stain removal either.
You are confusing rayon with polyester thread. Rayon is NOT bleach resistance while polyester is. Below is a link to a statement by Superior Threads documenting why they do not have a rayon thread line.
https://www.superiorthreads.com/e...
I read somewhere that their rayon thread was bleachable. I just don't remember where. Sounded crazy to me, but was hoping someone might be using this thread and let us know if the thread actually stood up to bleacing.