Why doesn't Inkscape recognize the Ubuntu color palettes?
Solution 1:
The problem is that the color palettes were not saved correctly. I have re-saved them in a proper format and put them on Ubuntu One.
Here are the files. In the archive there is now a readme file explaining the installation process as well.
Update
I've filed a bug against ubuntu-branding and sent a fix to be replaced with the currently available palette on design.canonical.com.