Because the screenshot only shows a small part of the image, I can only guess that the following is happening:
The area of the image that will remain visible is dimmed while you are dragging the crop handles. Once you release them the shading should disappear.
if this is not what is going on are you able to provide a bit more information:
Thanks for replying, Cari.
I figured it out: Unchecking "Highlight Color" in Forms got rid of it.
Preferences>Forms>Highlight Color> Uncheck.