After fixing the leak, if you don't want to repaint the whole ceiling, try touching it up with Kilz Upshot (kilz.com), an aerosol ceiling primer that's tinted to more closely match an aged white ceiling. Or if you prefer to redo everything ( and entertain yourself in the process), try Sherwin-Williams Visible Solutins ceiling paint. It goes on violet and dries bright white in 20 minutes, which ensures you don't miss any spots.
Info from Reader's Digest magazine. readersdigest.com

