Apply Vertex color to a Curtain_Curtain Moving

[javieroryan]

Hi all. I have a little problem, i was doing a curtain material.

I was using the World Position Offset input, for the movement of the curtain like this...(a.jpg)

But in order to function properly, i need to use the vertex color node and apply a vert color to the object / curtain.... i suppose that i need to use
the paint tools in the alpha channel? but i dont know how to do it.

please help, thanks