It *is* a problem...I *am* a doctor (allergist) and I'm always explaining to patients what this or that color on my fingers represents. They actually seem to be interested! Actually, what it does represent is forgetfulness. I have my wife buy latex gloves for me at Costco in multiple box lots, but I occasionally forget to put them on. They always work when used. No surprise, I guess. Sometimes waterless hand cleaner works after a memory lapse, especially for inletting black, but iron/vinegar stain and penetrating stains and dyes tend to seep into the skin layers and stay there until the skin renews itself. Fresh scars or finger tip splits tend to stain black and stay black with the stains and dyes. Any solvent good enough to remove most dyes and stains...like acetone...will also damage the skin and tends to cause more of the dreaded thumb tip splits. I do use it once in a while, holding the soaked piece of cloth in a *gloved* had to rub away a small spot on the other hand. You probably all know that vinegar will remove uncured epoxy from your hands.
Clay
San Jose