There was a dark feel because the backdrops were always black. Even when they added that big star thing it was still in front of a huge dark drape. In comparison to WWF/E, WWF always had the 'Tron that covered the backdrop. I assume you mean this WCW set too:
It was lit up like a tree when on, but you can see how much black there is in the surroundings. Even when they went to the video screen 'tron ripoffs, they were never as big as Vince's and still had the backdrops visible.
Aside the set, sometimes they would lower the "house lights" during matches as a lot of companies did/do so that a lot of the crowd was 'blacked' out while the main lighting emphasis was on the match.