The color that rubbed off your belt and onto your shirt can probably be removed by pretreating the stain first before washing. What you use to pretreat depends on what color the shirt is and what fabric the shirt is made of. If it’s white, and does not contain any spandex (also called Lycra and Elastane—check the care label to be sure) then you can use Clorox® Bleach Pen Gel to pretreat the stain prior to washing it. This is a great product that contains the same bleach active as Clorox® Regular Bleach2, but at a lower concentration that is safe to apply directly to fabric. It’s easy to use: right before you are going to wash the shirt, use the soft scrubber tip on the pen to apply a little of the gel directly to the stain, and rub it in. Immediately wash the shirt in the hottest water recommended on the garment care label using detergent and ½ cup Clorox® Regular Bleach2. Let the shirt air dry and check for success. Depending on how concentrated the discoloration is (probably from whatever dye was used to color your belt) the stain may come out with one treatment. More concentrated stains may require repeating the treatment for complete success, so it’s always a good idea to keep an item out of a hot dryer until you know the stain is all the way out.
For colored shirts (or white shirts that are made with spandex, even a small percentage), you can pretreat the stain with liquid Clorox2®. Just apply a little directly to the stain, and then wait 5-10 minutes before washing in the hottest water recommended on the care label using detergent and more Clorox2®. A heavy stain will likely need multiple treatments to get the dye all the way off, so again, be sure to let the shirt air dry and repeat the treatment if necessary.
Something else to consider is the belt: if it is a fabric belt that you can wash, you may want to do that to remove any excess dye, and help prevent color from rubbing off onto other items. If it’s leather, having the belt cleaned by a professional cleaner that specializes in leather can help.
I hope this is helpful! Please let me know if you have any other questions, and thanks again for writing.