In the editor viewport under the “view mode” drop down → “buffer visualization” there are both a base color and diffuse color modes. They seem to show the same image, what’s the difference between the two?
I’ve searched and have been unable to find a page in the documentation that covers all of the gbuffer/buffer visualization modes (at least on a single page). I think that would make a good addition to the documentation.
There’s a legacy mode of the renderer where it allows materials to specify diffuse color and specular color instead of Base color, specular intensity and metallic. The Diffuse color buffer visualization is from that.
The most important thing to use the GBuffer visualizations for is to make sure your materials are setup properly for physically based shading. For the most part this means you are making use of roughness properly - don’t just use a constant value across your scene, and metallic is set to 0 or 1 (not in between). See here