  The concept of transparent and opaque horizons is defined. One example of
opaqueness is the presence of a firewall. Two apparently contradictory
statements are reconciled: The overwhelming number of black hole states have
opaque horizons; and: All black holes formed by natural processes have
transparent horizons. A diagnostic is proposed for transparency, namely that
the computational complexity of the state be increasing with time. It is shown
that opaque horizons are extremely unstable and that the slightest perturbation
will make them transparent within a scrambling time.
