how to change ionic tab color from controller

I need to change the color of the ionic tab from controller , i have changed the tittle bar color from controller like this.. in html page i wrote ..

        <ion-nav-bar class="bar-positive" ng-style="{'background-color': viewColor}">
            <ion-nav-back-button></ion-nav-back-button>

         </ion-nav-bar>

and in controller i called ..

 $scope.$on('$ionicView.beforeEnter', function() {
     $rootScope.viewColor = 'green';
  });

and in css i wrote ..

    .nav-bar-block, .bar {
              background-color: inherit !important;
            }

In the same way can i change the color of the tab ... Is there any way to achieve it ?? Any help would be appreciated...

Thanks.

test this code,can use style Instead ng-style

<ion-nav-bar class="bar-positive" style="background-color:{{viewColor}}">
    <ion-nav-back-button></ion-nav-back-button>
</ion-nav-bar>

&

$scope.$on('$ionicView.beforeEnter', function() {
   $rootScope.viewColor = 'green';
});

or You can use an existing style in this url http://ionicframework.com/docs/components

for example green style for header

<div class="bar bar-header {{bar_style}}">
  <h1 class="title">bar-balanced</h1>
</div>

&

$scope.$on('$ionicView.beforeEnter', function() {
   $rootScope.bar_style = 'bar-balanced';
});