True Religion Green Cargo pants

Green Cargo pants from True Religion size 30 waist but honestly fits like a 31/32. Great pair of pants but as pictured there is a staining that occurred when I took these pants on vacation and put them in the wash with other peoples clothes SMH. Seems to be a tar like substance that I have honestly never tried to take out bc I don’t know how. Not really happy to sell them if anyone has advice it would help