Layer two PNG images and and having both full color Hi I've been at this for days and I'm sure there's a simple solution but being a bit of a blender novice I've not found it.

In this blender file Two PNG Layers I've got two png textures I'm trying to mix. The bit that is currently blue I'm going to make chrome (i just wanted it to be really obvious while i'm working on it). The problem I have is that using an add shader as the last step leaves the black skull layer opaque when I need them both solid. 

If I take either one of the mix shaders before the final add shader and go to the material output I get them solid but obviously just one image at a time. 

Thanks for any help
Copy your 'Black' image, and set it to 'Non-Color Data'
Put in the Mix Shader in place of the Add Shader, and plug the new image copy in as the factor.

You might want to keep your Add Shader for viewport work only.