Add 1 cup of salt and a packet of powdered fabric dye to a stainless steel basin or sink. Use a deep black tone that matches the hue of your shirt. You'll find such dyes in grocery stores, craft stores and many general merchandise retail stores.
Add 1 gallon of boiling hot water to the basin, stirring the solution with a plastic spoon until it disperses.
Dip a toothbrush into the solution and apply it to the surface of the stain. Scrub in circular motions to apply the dye into the fabric in one spot.
Alternatively, if your shirt has multiple bleach stains, dunk the entire thing into the solution. This completely redyes your shirt to cover up the light stains. Soak the shirt in this solution for up to 20 minutes.
Dump the solution down your sink drain and rinse the shirt in cold water for up to 15 minutes or until the water running from the shirt is clear. Launder your shirt with similar colors one time before wearing.