... that quickly facilitates the de-focusing of inverted selections (I.e., Capture screen, select portion of screen capture : press hot-key / click button : and (hopefully, although a default with a hot-key would be good) have options to choose from, to de-focus inverted selection - like reduced contrast, b&w conversion, etc.
update: Snagit is a commercial application that does what you want:
Irfanview portable. Press C to access the screen capture mode, timed or hotkey activated. It's a viewer that has many image manipulation functions as well.