Should I concern about RED objects in hierarchy view?

Just select your GameObject with the missing prefab connection and click GameObject --> "Break Prefab Instance" to remove the connection.

By "red objects", I assume you mean objects whose names appear in red in the Hierarchy window?

If so, that simply means that they were previously linked to a prefab, but the prefab has been deleted or somehow it has lost the connection. Unity is basically giving you a warning that for some reason, the object has lost its connection to the prefab without you explicitly deleting that connection.

It's not really a problem, but here's the only way I could find to "fix" it:

1. Create a new empty prefab
2. Link the object to the new prefab
3. Add a new component to the object (any component). A popup will appear, click Add
4. The objects name should now be black. You can now delete the component you added to the object, and the empty prefab.

I'd certainly be concerned about this because it means that you have deleted prefabs from your project which are now missing for objects in your scenes. If you're using those in many instances, you have to manually restore the connections (in the way that Stelimar described) - or live with the fact that the connection is gone for good.

So, I'd avoid having those "red objects" because in the long run, it'll make your project a big mess ;)

Well, thanks for all your answers, which are correct.

My concern was more about Apple approoval than engineering problems... As we have so many levels, they are working, so our concern is some kind of rejections for those Communist pieces !

If is not a problem at apple, ok with those!

Just drag and drop your Hierarchy object ( red name ) to Asset ... resolve the red name to normal color.