Vertex paint not working after sculpting with dyntopo on I started painted a low poly island model some weeks ago.  Today I modified the mesh with sculpt mode and when I activated Dyntopo, I got this warning:

Then I tried to vertex paint the new vertices but it is not working, the new vertices don't get painted. Here you can see my settings:

What I am doing wrong or missing to do? I will appreciate any help.
Blender is a complex application. I don't know exactly what I did, but at the point when I wrote my question, for some reason I had changed the Draw mode to Add instead of Mix. Once I put it back to Mix, it worked as expected and I was able to keep working in this project.