This PlMs.dat file is for Marth's data and shared textures

(These instructions sound complicated but I promise I'm just bad at condensing explanations)

To use it for the sword trail you can either replace your file with the one included I've only done this part in DAT Texture Wizard so the instructions for this part are for that
If you're using DAT Texture Wizard simply open your ISO and go to the Pl_.dat folder then dropdown the marth folder within the previous one and you should see at the top a file with the same name "PlMs.dat"
You can then click it and select import at which point you replace it with the file I've included and save the ISO

If you either want to customize the colors outside of the NB theme or have other modifications in Marth's data file you can open your existing file and go to the location in the screenshot I attached
Once you've gotten to the right lines you'll notice I highlighted a part in yellow and outlined one in red, the one in yellow is the first color and the one in red is the second 

I hope you enjoy the skin and if you want to follow a deranged person on twitter go to @S4ltfps