I believe it's a color dye from pants or a shirt that must have gotten wet and stained your clothes. You should take a shower to get rid of any dyes that are on your body - if you see a rash see the doctors. To get rid of the stain, use bleach and dip the clothing in wet water and let it air dry.
It's the only answer thats a place with official jobs. A normal farm would be there too, but a backyard farm is someones hobby and not a paying occupation, so OSHA isn't in charge of that.
