The only time I have ever personally experienced a black and white effect is when I got assimilated doing a Foundry. That's why I asked.
That's a funny thread actualy. I'm not doubting what you say, it's just that outside of that thread's OP, no other post confirms BORG for this event. I have played it soooo meny times and have not seen them yet. Weird.
Back on topic though, it just happened to me personaly with the enemy being Gorn. Further I am certain I witnessed it happen to another player VS Klingons, therefore the issue does not appear to be species specific.
I can confirm that there are Borg in this event. It only happened once and on the KDF side. I have read that, depending on the starbases level, diff types of enemy would spawn. So if Borg were to spawn, it must be a higher level base.
Also the level of the base for the mission is randomly chosen.