Like these ones above.
I thought they were called vertex colors but I guess not because I keep finding the wrong tutorials 
I believe you need a 3rd-party add-on to bake to vertex colors (I might be mistaken).
You can bake to an image without an image texture node attached to your base color node though, however you’ll still need:
- 1 UV node
- 1 Image Texture node
The bake setup directs Blender to which image to bake to, as well as which UV to use in the baking process.
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Thank you RPaladin 
I had found the solution from this tutorial
It’s basically what you explained done for each of the materials.
DPC