Hello polycount forum. As you can see i have a problem with creating modular assets in unity. The middle part has a darker shade then the corner parts. As far as i can tell, it looks like an issue the the normals. The mesh uses smooth shading, has no problems in blender. It has the same problem with unity default material…
Looks like you might want to UV this as a whole, not as individual parts. There's some mirroring between the left and middle parts. I would suggest UVing everything together, then split them up and use an Edge Split modifier so that you get some hard edges where you need it. Don't worry about the edges splitting, Unity…