Thank you Anton! I added the Alpha channel to the Vertex Color too.
I was working to get a solution about the scale and rotation of the mesh along the curve in this week. I think I am making some progress and I want to show the results of these days:
I changed a little the part of the User Interface where I create the planes, but now I think I am getting closer to something less restrictive than the previous method. Now I can scale the mesh along the curve using the graph but there is a couple of main issues that I need to resolve:
- I have to mid click to update the changes, it is not in realtime.
- As you can see, the graph is in another window and my idea is to have everything in the same UI. I am using QTDesigner to create the UI and I do not find the way to implement a graph in it.
I am having a hard time to fixed it, but I will keep trying. Rotation along the curve is working too by the way, but it has the same problems that the Scale graph. I hope to resolve all of this issues as soon as possible.
Let me know if you like the changes 
Keep the good work and have a good weekend everyone!