Hi,
currently in the viewport (not rendering), the diffuse color of a material is only shown in material shade mode.
A direct plugged in texture into the diffuse socket is displayed, but when the node setup gets more complex,
I end up with a complete black display of the object.
Switching to the solid mode results in not distinguishable all grey colored display.
When a scene gets more complex with a lot of different materials, at least for me, it gets a bit confusing.
So I added the option 'Viewport Color' from cycles into the material panel of the octane for blender plug-in,
as you can see in the picture below.
If anyone would find this useful and Otoy gives me the permission, I would post here or send the changed ui script to JimStar.
Happy Blending, Volker