INCREASING THE CROP TOOL’S OPACITY
There are times that you want to see what your finished product will look like once you crop it. The best way to see that is to have a black background. To do that, once you have clicked-and-dragged out your crop border, increase the Opacity in the Options Bar to 100 percent. This will make the area to be cropped away completely black, and will allow you to see what your finished product will look like.