I washed my black underwear and now one of my black socks looks brownish on one side. How do I return the sock to its original black?

cotton and polyester puma sock I washed with some pooped underwear, so I don't know if this sock looks brownish due to fecal matter.

I used a cold cycle and abundant detergent. Every other undie looks fine.

I don't know if I should leave the piece to rinse in a cold water bucket with some detergent and wash again.