Decal problem

I have this dome model that I created in Maya by creating two hemi-spheres with one of them being slightly smaller and I used the boolean difference tool to empty out the inside to make it indoor.

I want to put a decal indoors but it doesn’t do what I want it to do. It always render on the outside of the dome.

From inside:

From outside:

Any ideas on how I can make this work?

I think it’s to do with the normals, no? Are the normals on the inside pointing inwards?