I used to get it a lot from the Dosko too, and you'll get it changing the teeth over, mine tend to go a redish brown, the tanin colours of cocos palms.
What you are getting is tanin stains, aboriginals paint with the stuff mate, maybe in 40,000AD it will wear off.
Not even petrol, acetone, metho, kero, windex, gumption etc gets it off, it's in your skin like a tattoo.
Wear gloves, I like the suede type leather ones, I get it a little from the levers of the Kanga too, depends on sweat and amount of dust.
Ever had the chipper out in the rain at night, then you park it on the customers driveway and start it ... it drips black drops of goo the same, tanins mate.
Cocos palms is reddish and a week easy for it to go.