Blue marks on clothes after washing: what they are and how to get them out

• 240 ml vinegar to 0.95 L water
• Soak 1 h

The American Cleaning Institute's fix for blue detergent stains: [1]

1. Add 1 cup (240 ml) of white vinegar to 1 quart (0.95 litres) of water in a plastic container.
2. Soak the item for one hour.
3. Rinse.

In The Wash gives a similar mix (one part distilled white vinegar to four parts warm water) and suggests gently rubbing the marked fabric between your fingers every 10 minutes during the hour, then washing with detergent and checking again. [4]

For white powder streaks on dark or bright clothes, the American Cleaning Institute suggests a weaker soak: 1 cup (240 ml) of white vinegar in 1 gallon (3.8 litres) of warm water, then rinse. [1]

Blue-grey, greasy-looking marks usually come from undiluted fabric conditioner landing directly on the fabric, or from using too much. [3]

1. Dampen the mark.
2. Rub it with a bar of soap.
3. Rinse, then wash as usual. [1][2][3]

If it's still there, University of Georgia Extension suggests soaking the mark in concentrated detergent and water, then washing in hot water (if the label allows). [3]