Well, this is certainly a development.

You can thank NightFox for this; they developed a modding tool and mod manager for Them's Fightin' Herds: Velvet Beautifer. Frostbringer also made a mod for it, the Pony Palette Pack #1, which is the mod these images use.
Altered palettes are here: >>3553758

I have known of NightFox for some time before this, but only just recently did I actually find out about the Palette mod, which is why I didn't post anything about this before; there wasn't anything to do with it.

Here is the GitHub page for the tool: https://github.com/ThemModdingHerds/velvet-beautifier

Now, there are two different versions of this tool; a command line version (CLI) and one with a ui (GUI), but I can't manage to make the GUI one work, with some crashes relating to gtk-3, or something, so I'll run down how to install and use the mod manager, with the Pony Paletts as an example.

How to install mods with VelvetBeautifierCLI

1. Download VelvetBeautifier CLI
   GitHub source: https://github.com/ThemModdingHerds/velvet-beautifier/releases/tag/2.3.1
   GameBanana source: https://gamebanana.com/tools/15674

2. Extract VelvetBeautifier into a folder

3. Create Mods folder within VelvetBeautifer folder

4. Download mod

5. Extract mod from archive to get folder, and put it Mods folder
   ex. "ponypalettepack1v1_138d9.zip" contains "Pony Palette Pack #1 v1.0",
   end result is VelvetBeautifer\Mods\Pony Palette Pack #1 v1.0

6. Open command prompt

7. Change directory to VelvetBeautifer folder
   ex. >cd "C:\Users\EpicG\Downloads\VelvetBeautifier"

8. Launch VelvetBeautifer

   VelvetBeautifier.CLI

9. Install mod

   VelvetBeautifier.CLI --install Mods[Mod folder]
   ex. >VelvetBeautifier.CLI --install Mods\Pony Palette Pack #1 v1.0

   Here, take note of what the command says. The prompt should say something like:
   Velvet Beautifier v2.3.1.0

   
   

   A Mod Loader/Tool for Them's Fightin' Herds
   installing folder at Pony Palette Pack #1 v1.0...
   installing mod 'frost.tfh.3p1'...
   This 'frost.tfh.3p1' (without quote marks) is the id of the mod, and will be needed.

   1. Enable mod >VelvetBeautifier.CLI --enable [mod id] ex. >VelvetBeautifier.CLI --enable frost.tfh.3p1
   2. Apply mods >VelvetBeautifier.CLI --apply
   3. Launch game

Some other useful notes:

To disable all mods, use command --revert
ex. >VelvetBeautifier.CLI --revert

To disable a single mod, use command --disable [mod id]
ex. >VelvetBeautifier.CLI --disable frost.tfh.3p1

To list currently installed mods, and whether they are enabled or not, use command --list
ex. >VelvetBeautifier.CLI --list

Keep in mind, whenever you enable/disable a mod, you need to APPLY that change (see step 11) before you can run the mod in game!
Also, this mod manager keeps a backup of all the main data files for the game, so expect your drive to get filled up by an extra 6 GB when first launching this app.

More details about the mod and how to use it are on the GitHub source page.