This is a tannin stain - a plant component that often shows as a color in the final product. Fresh tannin stains can usually be removed by laundering the garment using detergent in the hottest water recommended for the fabric.
Never use natural soap in a bar or soap flakes because they make tannin stains more difficult to remove.
If the garment is dry clean only, point out and identify the stain to your professional cleaner. If you are using a home dry cleaning kit, be sure to treat the stain with the provided stain remover before putting the garment in the dryer bag.
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