We can't literally block it from receiving light. However, we can set up the shader so that it does not take any light into account in its calculation.

The Poser root node Diffuse_Color is a Diffuse node, which has its primary purpose being to take light into its calculation. So it follows that you should not be using that.

Instead, plug the texture into the Ambient_Color and adjust brightness with the Ambient_Value, or plug the texture into Alternate_Diffuse, which doesn't add a lighting calculation as it is expecting you to supply on as a node. If you don't supply one then it doesn't do one.

In other words, do what seachnasaigh said, and what I've shown you for nine years in the BB Environment Sphere.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)