Darken Camera Layers separatly.

Hello, I want to darken layers for the camera separately so I can have one layer still being lit. I don't want to darken them per say I just want them to turn black gradually.

Since I want one layer to be lit and visible I can't use a GUI-texture or use fog to achieve it.

Is there a way to just tint the layers or access the textures? I imagine it would be possible to achieve a similar effect by just darkening the light and having the lit layer have unlit shaders but I would prefer another option.

Thanks in advance!