The International Space Station has several cameras cameras mounted on it. The video from them is streamed live. You can see the live stream here

But you can also see the location of the Space Station at the same time. The station orbits Earth every ninety minutes, so it will often be in the dark. When there's a black screen, that's what's happening. The view is also being switched from camera to camera, so this can cause a grey screen, as also happens if the communications downlink isn't available.