analog

As a man who wears nothing but black- and has black bedsheets- I can tell you that all you need is spit, or water and a little soap. If you find one after it's dried, just drop a little spit (i'm not joking) on it and rub it in. Don't let it air dry, wipe it dry with something. No effort, and it'll disappear.

Of course, you could always just wash the sheets the next day. Why would you let it just sit there forever?