Rusty bleach spots on black Serenity pants

Serenity pants are stretchy yoga/exercise pants. Mine are black. I accidentally washed them with a white top that had a stain I’d soaked with bleach. The bleach left some rust colored spots on my black Padagonia Serenity pants. Is there a dye for this kind of material I can use?

Thanks.

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look at the tag, whats the material its made from?

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they are 85% organic cotton/15% spandex. (no longer sold at Patagonia, but here's the link for what they look like https://www.rei.com/product/796906/patag... )

Rit dye web page says it doesn't work on spandex or bleach damage.

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