You might also check the existence of '/usr/share/create/swatches/*' (possibly used by software like Agave). A quick test shows that Inkscape loads palettes stored in the 'share/create/swatches' directory and lists them below its own shared palettes loaded from 'share/inkscape/palettes'.
from 'src/path_prefix.h':
# define CREATE_PALETTESDIR INKSCAPE_DATADIR "/create/swatches"
You might also check the existence of '/usr/share/ create/ swatches/ *' (possibly used by software like Agave). A quick test shows that Inkscape loads palettes stored in the 'share/ create/ swatches' directory and lists them below its own shared palettes loaded from 'share/ inkscape/ palettes' .
from 'src/path_ prefix. h':
# define CREATE_PALETTESDIR INKSCAPE_DATADIR "/create/swatches"