I really don't see the damage in releasing a sepia version of the picture. Why should I care that it's inaccurate? It's a postcard from the other end of the solar system.
As an example, here's an actual true-color image of the earth: http://imgur.com/EEt635V.jpg
And here's a "true-color" image of Earth, produced using the New Horizons / Huygens colorization technique of combining a greyscale image with very low-resolution color data: http://imgur.com/IOqOTyw.jpg
What's wrong with this? A.) It flat-out isn't "true-color", and NASA shouldn't be spreading inaccurate information, and B.) It's arguably a more boring image than the greyscale original (http://imgur.com/hwYA6VK.jpg), which leaves one better able to imagine possible color schemes, rather than fixating one upon a single, inaccurate, and very boring color scheme.