How do you set dye in black cotton fabric?
My mother-in-law told me that you can pour 1 cup of vinegar in
with your clothes to set the color. I've never tried it, but she
has. After you put your clothes in to wash and the tub has filled,
stop the washer and pour in vinegar. Let it soak for 10-15 minutes,
and then continue washing. You'll have to wash again afterwards to
remove the vinegar smell.