Shader turns black when connected to node group

Question

I have a project where I reuse the same material for multiple things. So, I use node groups; saves a lot of trouble - at first!

Up to this problem I have with node groups:

In 1 you can see, that the logo (white text) is on a black background. This black background should be a node group (and certainly not black).

Here is the Logo Overlay node group:

If I put the node group "ultramarinblau" into the Logo Overlay node group, it does not work!

Only if I add the "ultramarinblau"-node group directly into the Logo Overlay node group, it works:

This behavior is not desired. I'd like to reuse my Logo Overlay node group multiple times with a different node group-input.

What am I doing wrong? Or could this be a limitation of Cycles node groups?

Any ideas are appreciated!

Answer 1

This is because you are plugging a Shader output (green) into a color input (yellow). See What is the meaning of the color of the node sockets in the node editor?

Instead you should add a shader input (green) to the "Logo Overlay" group. Doing this is a little complicated, as you currently can't directly set the socket type without some python. However, it is possible:

1. Enter the node group (↹ Tab)

2. Plug the placeholder output of the Group Input node (hollow) into any input socket of the desired type. In this case, green for shader:

   

   Optionally rename the new input in the properties panel (N).

Once this is done, your setup should work.

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I don't recommend putting the material output node inside a node group, as this could lead to confusion down the road depending on how the group is used. Instead you might want to plug the mix shader into a Group Output node, and plug the entire group node into the material output in the main node tree.