Imagine the following: you’re in Vertex Mode, coloring your object nicely. When it’s all set and done, you lean back and select Viewport Shading or Rendered View.
And what do you see?
What happened to your Vertex Paint?!
Well it’s very simple, luckily. By default, your Vertex Paint is added to a layer called Col. You can find this udner Vertex Colors in your Object Data Properties tab (triangle).
Now, all you have to do is add an Attribute node, enter ‘Col’ in the ‘Name:’ field and connect the Color to your Color shader.
This is Mari’s note to herself. This note may or may not be useful for you. It is intended as a personal note, publicly shared in case someone else finds a use for it as well.