I would submit a pull request, but I don't think that's even warranted for one line of code. also, I'm not sure of the palette on the new Kindle, though I am guessing it is more similar to that on the Kindle 4. Also, I'm no python programmer, and this is all I can really offer. Hopefully in the future I can do more.
For now, though, adding this to the Profiles section of mangle/images.py:
'Kindle Paperwhite': ((758, 1024), Palette15b),
Thank you, and keep up the good work.
Updated profile for Kindle Paperwhite
As per issue #10