What has actually happened is that many teams have adopted black/grey as an alternate jersey color; some of the bigger teams will also have multiple helmet colors. From there, teams generally have discretion to mix and match each week (and they frequently delegate this decision to players).
"Blackout" games as such may be less frequent, but it's absolutely the case that teams are frequently wearing black/grey alternates and black helmets (or primary-color helmets with black/grey decals) on a regular basis.
Add to that the fact that this Saturday's slate of games actually falls on Halloween, and you have an ideal opportunity to roll out a black & royal alternate.