ColourDNA is a social networking site that aims to help you find new things that you'll like. You start by logging on and selecting your favourite colour. You then use this colour to tag different things that you like or want to recommend to others.
The service uses your personal recommendations to match you with others that have similar tastes. Stuff that they have discovered, but you haven’t, are then recommended to you. The iPhone app is basically a neat mobile interface into the site's recommendation engine and is pretty easy to use. It adds in location based matching, as well as a Foursquare-style Check In system.
Its colour coded matching seems a bit of an odd way to approach what is essentially a social recommendation engine, but ColourDNA is interesting enough to make it worth giving a whirl.