it's been a while since this came up, and while there are options out there, i accidentally yellowed the crotch of a pair of pants with a particular brand/formulation of iodine spray which has turned out not to be good for my skin [sticking with my usual brand, thanks] and stained my skin for days.
the brand is Battles and the formulation is Iodine and Potassium Iodide in Propan-2-ol.
anyway, inspired, i decided to try it on a pair of unused pants as i wasn't too sure if the combination of skin oil, creams and soaps hadn't made the other pants readier to take up a stain.
straight after staining and still a bit brown.
washed and dried. it should become more subtle after a few wears and washes.
one thing to note is the fumes given off during staining. i think that next time i'll do it outside and whilst wearing a mask with charcoal filters.