How Does the "Copy From Vertex Color" Option Work?

In the Active Cloth Paint mode in the character mesh window, there is an option called Copy From Vertex Color used for creating masks for cloth simulation. How do I use it? Is it referring to the Material Editor? Do I use it by attaching a grayscale map to a color channel in the Materials Editor? How exactly do I set it up?

The UE4 Documentation on this does not explain this very well.

It references vertex colors, which come from vertex maps. You can paint vertex maps in 3D apps (such as Maya or C4D) - or you can paint them inside of UE using the Paint mode. When importing FBX files that contain vertex color maps do this:

FBX import options > Mesh > Advanced. Set Vertex Color Import Options to Replace.

Thanks for this, However Im trying to find the same thing with the Alembic file, I created a simulation in c4d and make some texture maps for velocity, age, speed… When I created a blend material in Unreal using Lerp, and vertex color as alpha… It did automatically loaded 1 Texture Map, however I need to use the other 2. How can I access them ? Please help.

In .25.2 the option doesn’t work.
Vertex paint is present on the mesh and can be visualized, for instance in my case it fades from red to black.
importing the red channel should therefor show some gradient results. Instead the mesh is just painted to 0 values - b black, not pink.

Ok, an amend to that.
The copy function DOES work, but it keeps on using whatever data was already in place BEFORE you created the cloth data.
So the vertex data isn’t changed by simply re-importing the cloth.
That means that for every change you have to delete the cloth data, import, and re-create… painful.