Anytime I add a tab bar controller to XCode the tab bar is greyed out and I can't see any of the tabs in the storyboard. At runtime it displays fine. I can't figure out why it is happening.
Add an image to the Tab Bar Item and you will see the normal view of the tab bar on the specific View Controller where you changed it. When every single Tab Bar Item got an image you will also see the normal appearance in your Tab Bar Controller.
Setting an image for the Tab Bar Items and restarting xcode fixed it for me.
In the assets folder (or wherever your image is kept), set 'Render as' to Original image
It looks like this was a bug in the XCode UI. This has been fixed in later versions of XCode.
来源：https://stackoverflow.com/questions/27927244/xcode-6-tab-bar-tabs-greyed-out