Chlorine bleach potentially does two things to nylon carpet fiber. First, it removes color – that’s obvious. Second, it may damage the polymer dye sites, depending on how concentrated it was when spilled. With wool, the fiber may be dissolved or significantly damaged.
If diluted bleach was spilled on the carpet, chances are good that it can be neutralized (this is essential) and re-dyed with appropriate dye stuffs. However, it takes a trained and experienced technician to re-dye carpet to the correct hue color) and shade (grayness), without circles or a variety of other problems.