Every day is sunshine and it never rains.
At first, they can't believe it and figure maybe they're suffering some kind of hallucination. Then they start to appreciate things like the weather always being 72 degrees, and the streets being always clean, almost no noise. They realize more and more that this sanitized world also has no joy, rage, passion, or intellect. And no change. The teens have brought with them their 90's sensibilities and slowly start to introduce change into this colorless world.