Do we know that dark matter is 100.00000% invisible?

It depends on the definition of invisible. Dark matter is invisible at the level of an LHC detector. It will leave no track in it. We will just 'see' something missing (deduced from energy conservation). Dark matter is also not electromagnetically interacting. In this way, it could be seen as invisible as electromagnetism is connected to light.

I assume I more or less answered the second question too, didn't I? :)