Maybe some of you know that there's a voxel editor called Goxel. Sadly it's original author is a total j*rk, so just a heads-up, this has been forked and expanded as it should have been!
https://goxel2.github.io/
And the good news is, among other this, this fork supports Minetest MTS schematics! :-) And Minecraft NBTs (old format and new Sponge format as well), OpenSpades (Ace of Spades free clone), etc. which are not handled by the original.

The MTS importer uses special GIMP Palettes (handled by Goxel2 internally) where the color names are actually node names, simple as that. Goxel2 comes with a default Minetest Game palette and a Mineclone2 palette, but you're free to add whatever you need.
Cheers,
bzt
ps: I'm not the maintainer of Goxel2, I've just implemented MTS import in it.