Project Ara will focus greatly on customization. According to project leader Paul Eremenko, the phone will ship in a dull grey color to encourage people to personalize the device.
Project Ara will run on a version of Android and Eremenko said that the OS will be updated to support the smartphone's modules sometime in December, just before the first product is released. The physical skeleton that it will use to hold each module is supposed to last from five to six years, and each module is attached via electro-permanent magnets. Third party developers will be able to create their own modules and then manufacture them by using a 3D printer.
Source: Neowin