If you're trying to use this pack in Unity, you need to make a shader for vector colors, using this code. Then on the .blend file in Unity, you click extract materials and put them wherever you want. Apply the vector colors shader you made to all the materials. Once you put the .blend file in the scene, it should already have the materials applied appropriately. This should work for all of David's projects (assuming they all use vector colors). I did this on Unity 2020.2.5f1. I'm hoping David can add these instructions on the website because it only has instructions for Blender and Maya. Also, the assets are dope, thanks for your hard work.
Edit: This works for the .fbx file too. As it's stated in the description, it's the master file so use that instead.