Use a Bleach Alternative
"Before reaching for bleach (which can actually damage your fabric) to save towels that have lost their bright white luster, try the baking soda and vinegar approach for an alternative fix. Add 1/2 cup of baking soda to the washing machine with your preferred detergent. Then add 1/2 cup of distilled white vinegar during the rinse cycle. When you're done, your towels will look like you dried them in the warm Summer sun."