Article in English: During the rinse cycle, add 1 cup (250 ml) of white distilled vinegar. Add the vinegar directly to the washing machine basin containing the black clothes; do not add it to the detergent slot, if a separate slot exists.  Adding vinegar to the rinse cycle has several benefits, including those that pertain to preserving black clothes. This household miracle fix can set colors and also strip fabric of detergent residue. That residue can otherwise create a film on your clothes, making the color appear faded. Vinegar is also a natural clothing softener. The vinegar should evaporate during the rinse cycle, so usually, no smell will be left behind. If a smell does linger, however, air drying the clothes should get rid of it. Add 1/2 cup (125 ml) of table salt to the wash cycle alongside your black clothes. The salt should be placed directly in the main tub of the machine and not in a separate compartment. Salt can help prevent color dyes, including black dye, from bleeding. It is especially helpful when used on new clothes, but it can help restore the color of old clothes by rubbing off detergent residue. Simply add 1 to 2 tsp (5 to 10 ml) of black pepper into the washing machine tub along with the black clothes at the start of the wash cycle. Do not add any to a separate detergent compartment if one exists.  The abrasiveness of black pepper strips away residue responsible for some of the fading, and the black tint of the pepper can help strengthen the dark hue of the dye. The black pepper should wash out during the rinse cycle. Sprinkle 1/2 cup (125 ml) baking soda to the washing machine tub after you fill it with the black clothes you want to preserve. The baking soda should be in the same portion of the machine as the clothes. Wash the load of laundry as usual from that point on. Baking soda is commonly used to help brighten whites as a form of non-chlorine bleach. As a non-chlorine bleach, however, it can also be used to brighten other colors, including black. Brew 2 cups (500 ml) of coffee or black tea. Add this...

Summary in Chinese:
洗衣服时加点醋。 用盐。 撒点黑胡椒粉。 加入烘培用苏打粉。 利用咖啡或者茶。