Compose not seeing layers

[Ofnuts]

How do you save your "old" projects? If you don' t save them as XCF the layers are lost.

Otherwise you can work with a setup like this:

• The Groups and "Blue" are in "Addition" mode
  
• The Groups are made of a Color layer in "Multiply" mode, plus your actual work layer (in "Normal" mode)
  
• At the bottom the layer mask of the Alpha layer dictates the alpha channel of the whole image
  

   

To work on a specific layer more comfortably you can make most of the rest invisible:

   

You can also split an existing TGA into a similar setup if necessary (but I have no time to describe how right now).

See XCF attached.