my bad..that was silly..! Just need to add ui config to navigationBar config property in the code...does the job now.
Ext.define('MobileApp.view.Offers.OffersNewNavigationView', {
extend: 'Ext.navigation.View',
xtype: 'offersnewnavigationview',
config: {
fullscreen: true,
height: '100%',
autoDestroy: false,
defaultBackButtonText: '',
navigationBar: {
ui:'light',
items: [{
align: 'left',
id: 'newSlideBut',
iconCls: 'list',
ui: 'plain'
}
]
},
items: [
{
xtype: 'offersnewdataview'
}]
}
});