I have done this before, but that was before the principled BSDF shader existed. Now I'm trying to do a similar node setup with the principled BSDF shader instead of the diffuse BSDF shader, but the result is not 100% perfect! The background of the mesh with the transparent decal image, differ slightly compared to the surrounding mesh. I want the background around the decal to be fully transparent and look just like the nearby meshes.
The principled BSDF shader to the left in the image below has the green color for that background and that is the green color I also use on the rest of the object with the same settings.
Is there a better way to achieve this with a better node setup or just adjust my node setup in some way? I have tried to adjust the value of the mix shader, but without any improvement.