This is a new feature in DNN 7 that dims the page when in edit mode, and then un-dims the module you hover over with your mouse. This seems pretty cool at first, but can be annoying for some people. Here is how to turn it off for a portal.

Add this class to the bottom of your Site Settings Stylesheet Editor or your skin.css file.

.dnnEditState .DnnModule {
opacity: 1.0;
}