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.
Did you use bleach in the wash? If it’s a light brown looking spot on black fabric that’s clearly lighter than the surrounding fabric, that’s my guess.