Technically this depends on a resort - in Aspen or Squaw Valley a double black diamond is in the "insane" level category, much steeper/challenging than even the black FIS slope in Sölden. I remember the lift sign in Squaw Valley's Headwall/Palisades - "Experts only. No easy way down.", and it was like that. Maybe upper part of Hahnenkamm could be comparable ;-) Usually double black diamond corresponds to European free ride zones near steep ridges.