Alpha in 2D game texture - Unity

Question

I want to add a background to my 2D game. The full-image has transparent areas, and I also want to set the alpha of the opaque ones. It is a texture, I need to change the offset of this for the parallax effect. I am looking for a solution to do this. I've tried with a quad but I could not set the alpha. Do I need to set the alpha before in Photoshop ? Thanks!

Answer 1

I've realized that Unity has an option to do that, I've just selected Legacy Shaders/Transparent/Diffuse.