Per Nike's press release:
The "Day to Night" collection celebrates runners whenever they choose to run – at twilight, sunset and everything in between. Each of the colors is inspired by a shade of the sky, from dawn to dusk, and allows runners to – for the first time – make a statement by matching their Apple Watch Nike+ bands to their footwear.
These bands will go on sale on June 1 for $49. These look great; I'll definitely be getting one. I have a Nike+ band and like it a lot, so these new ones are exciting.