If you need to set a number of vertices to a specific color, it’s not obvious how to do this (at least not for me).
- Select the vertices edges or faces in edit mode.
- Switch to Vertex pain and click the icon that says Face selection masking (it’s between the layers and pivot point settings).
- Select a color
- Hit space and search for set vertex color.
This is great if you want to use Vertex colors to mark different areas of an object.