Been there. Done that. I decant the Blu-kote into a small bottle and use a Q-tip dipped into it to paint the solution on the skin. Beware of treating combs. Wear a rain coat. The chicken will feel the cold wetness and shake their head, sprinkling you liberally in the face with the purple stuff.
If you want to get rid of the stain quickly, rub sink cleanser with bleach into the stains, but rinse it off quickly so it doesn't eat your skin off.
I don't know if you have such things in the US but I use a Green Pad that you scrub dishes with for stuff like that. Failing that a drop of rubbing alcohol and a cloth should shift it.