Here are some ideas to expand RadarWatcherX; try these on your own.
Add slider controls to the document window to adjust the sensitivity of the closeColors option. Adding one for hue and one for brightness sensitivity should do the trick and make the application more controllable, depending on the maps the user chooses.
Add the ability to make more than one watch box in a document. Multiple watch boxes with their own color selections could really expand the usefulness of the application.
Add the ability to email a user as an alert option. You can use the -deliverMessage:subject:to: method of the NSMailDelivery class in Apple's Message framework located in /System/Library/Frameworks. Although no formal documentation exists for this framework, extensive notes are in the header file. While you're there, look at the header files from other frameworks you don't recognize. You can learn a lot by poking around (read-only) in the depths of your system's directory structure!