Hi there!
First of all, make sure you have the latest versions of the Choice Manager and Eli Book plugin. The demo sample project is just a sample project, so maybe it does not have the latest versions.
Normally that can happen because the window image is not fully loaded and the \c[] escape character gets the color from the window file. So since the window is not loaded, it "returns" black.
But I also need to see how you are doing this. Can you show a screenshot of the plugin command?
I tried this below and it worked just fine: