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Don't use warm or hot water to wash your color-dyed fabrics. Choose the cold water setting, and use a color brightening laundry detergent. Pour in 1/2 cup of baking soda while your machine is on the wash cycle. Alternately, use a liquid laundry detergent with baking soda in it. Baking soda helps dyed fabrics to stay bright. As a bonus, baking soda can also tackle washing machine odor! Add 1/4 cup of white vinegar for a small load, or 1/2 cup for a large load. Use this technique to help colors stay vivid, and also as a natural fabric softener. Vinegar softens fabric by dissolving mineral, soap and residue build-up. Vinegar is also anti-microbial and safer than chemicals.

Summary:
Wash your fabrics in cold water. Add baking soda to your washing machine. Pour in vinegar during the rinse cycle.