Interesting

I tested a swatch of one of the polyester fabrics in my fabric stash to see what would happen. As I more or less expected, what happened was nothing at all; the color is built into the fibers.

Later on, I made a skirt out of that fabric, and dyed it with a dye for synthetic fabrics.

Still later, I accidentally dripped some chlorine bleach on the skirt. I don't seem to be able to use bleach without getting some of it on my clothing. The bleach removed the dye, leaving the original color in those spots. This may be useful for later textile projects.