Any suggestions for a stain? One of my delicate pink shirts has a mystery stain on it....

One of my delicate pink shirts has a mystery stain on it. It looks close to it could be chocolate, blood, or even coffee. I've tried bleach pens to no avail. The shirt is 92% cotton and 8% Spandex. The tag say "Hand Wash Cold, Light Tumble Dry". Help?
Paint? does it come out?
Answers:    Try salt and white vinegar.
I own a t-shirt beside sleeves that are...
Soak for a long time in Oxyclean. But you might pre-treat it first near peroxide. Then wash as usual. Oxyclean can be dissolved in Warm river, then allowed to cool before calculation the shirt. Oxyclean also makes a pre wash spray.
Pee on the mattress??
spray and clean