The best way to remove fresh water-based paint from clothing is to sponge the stain with a solution of water and liquid hand dishwashing detergent or liquid laundry detergent. Mix one part water with one part liquid detergent.
Use a dull knife or spoon to scrape off as much of the excess paint as possible. Blot gently with a cloth. Avoid allowing the paint to dry, as this will make it more difficult to remove.
Working from the wrong side of the fabric, flush the paint stain with a strong stream of warm running water. Gently work the detergent solution directly onto the stain, using a sponge and rubbing the fabric between your fingers. Rinse the stain thoroughly with warm water. Continue to repeatedly sponge and rinse the stain until all or most of the paint is gone.
If necessary, blot with rubbing alcohol or nail polish remover on an absorbent cloth to remove any remaining paint. However, such products should not be used on fabrics containing acetate or triacetate. The clothing can then be laundered as usual.
This method can be used to remove water-based and acrylic paint stains from washable fabrics. Dry-clean only clothing should be taken to a reputable dry cleaner to determine if stain removal is possible.