Adding new tabs to a tab bar controller
First drag A TabBarController from Object Library you see that only two tabs with thier VC there.
to add more Tab Item in TabBarVC drag VC from Object Library
Then Control drag from TabBarVC to Newly VC then Segue relation pop ups
Select last one Relationship Segue -> View Controllers
I had the same problem until I added a tab bar item from the object library into the new view (settings its attributes on the right hand panel) and THEN ctrl dragged from the tab bar controller to the new view, creating a relationship segue.
If I tried to ctrl drag from the tab controller without first adding a tab item to the new view, it had the behaviour you described.
be sure to check the size of your icon image.the tint of image added is grey by default. If you have a large sized tab bar image, it can look like the whole tab bar is greyed out for some reason. pic does not auto resize.