so i found the time to work with your numbers today
FYI: my tftd palettes were slightly wrong - i fixed that
here the result
i used the bigobs as a compare image in the hope that a lot of the colors are used
first part = original image (tftd depth0 palette)
second part:
first i show the ufo battlescape palette and the tftd-colors i assigned to each ufo color (according to your numbers - at the attached compare image i cut a bit of at the black colors it was long (>16 slightly different black colors))
next the bigobs converted according to the color-assignemnt showed above
third part:
first i show the ufo battlescape palette and the tftd-colors i assigned to each ufo color manually (i also cut a bit of at the black colors)
next the bigobs converted according to the color-assignemnt showed above
you can see differences in some cases:
the automatic coloring makes a better color substitution then the manual
sometimes its a matter of opinion (autocannon yellow => green or brown color)
main negative of the automatic conversion: a lot of strange spots/"impurities" easily visible in the corpses
for me it seems manual trumps automatic color assignments not necessarily in regard to color similarity but in less fixing work after conversion