Select or deselect tab bar item

Hello Friends

I need work using tab bar item, but when I touch in a tab bar item the item change the color to blue, I need when I touch again, the item back to gray. To verify what the item is clicked I use this code:

func tabBar(tabBar: UITabBar!, didSelectItem item: UITabBarItem!) {
     switch item.tag  {
          case 0:
               //if item is selected, so back the gray color and deselect
               break
          case 1:
               //do something
               break
          default:
               //do something
               break
     }

Whats the line command tha I should put in my case function to select or deselect the item ? Or there is other way to do it?