The best thing about Flair pen ink stains is that they're water-soluble and can be removed a bit more easily than ball-point pen ink or permanent marker. Stains on washable clothing like cotton can be treated the same way as non-washable clothing, according to Cornell University's Cooperative Extension. As with any stain, removal works best when the stain is fresh. Keep the cotton clothing away from heat, which tends to make stains quickly set.
Place the stained cotton on a flat, sealed surface like a kitchen countertop. Pour 1 tsp. dry-cleaning solvent onto an absorbent sponge.
Blot the stain with the sponge, using different areas of the sponge each time you blot. Turn the cotton fabric over to blot the stain on both sides.
Dot the stained area with mineral oil to further loosen the Flair pen ink. Blot again with dry-cleaning solvent, then pour solvent directly through the stained area to rinse it completely.
Launder as usual, in warm water with detergent. Examine the cotton fabric for traces of stain while the cloth is wet. If traces of the stain remain, mix 1 tsp. bleach with 1 tbsp. water. Drop the solution onto the stain with an eyedropper and let it sit for 30 seconds. Rinse thoroughly with water.
Mix 1/3 cup white vinegar with 2/3 cup water and rinse away any remaining bleach residue on the cloth. Launder again.