Here’s the ISS HD Earth Viewing Experiment. The experiment was activated on 30 April 2014 and has worked quite well.
The UStream page tells more of the experiment and answers like: who do I see a black or gray screen.
NASA and JSC have a nice page with the video, a plot of the ISS location and a Google map of what’s under the ISS. Have a look.
When we had the shuttle missions NASA would often show television video of the Earth as the shuttle orbited. Frequently it was the best programming on TV. I need to watch as the ISS passes over thunderstorms in the dark areas to see if the HD camera picks up the lightning flashes.