I get the feeling that people are confusing vibrant colors and sunlight as meaning the world somehow isn't dangerous or dystopian, as well as confusing conceptual darkness with literal darkness. The best way to describe the way we saw Night City portrayed in the E3 trailer video and E3 demo video is that it is a
Crapsaccharine World. The 'brightness' of the city during the daylight hours covers it with a layer of false hope that makes it believable as a place that people would be convinced into coming to and try to start a new life there - oblivious to the danger.
As the E3 trailer video describes it, it's a city of dreams. A city that always has a promise for you, but that might be a lie or an illusion. You don't get that kind of sense from a city that is visually portrayed as some bleak, bland, dreary, foggy, somehow-always-nighttime crapsack of a place. After all, there is no darkness without light, no despair without hope; you need both in order for it to work.