打开微信小程序，底部TabBar选中的菜单项出现淡蓝色的底色，使用的是原生TabBar并没有自定义，请问是什么原因？

app.json中的tabBar配置如下：

"tabBar": {
    "selectedColor": "#2F78FF",
    "borderStyle": "white",
    "backgroundColor": "#ffffff",
    "color": "#CCCCCC",
    "list": [
      {
        "text": "圈子",
        "pagePath": "pages/main/main",
        "iconPath": "images/tab_bar_circle_default.png",
        "selectedIconPath": "images/tab_bar_circle_selected.png"
      },
      {
        "text": "消息",
        "pagePath": "pages/message/message",
        "iconPath": "images/tab_bar_message_default.png",
        "selectedIconPath": "images/tab_bar_message_selected.png"
      },
      {
        "text": "我",
        "pagePath": "pages/me/me",
        "iconPath": "images/tab_bar_me_default.png",
        "selectedIconPath": "images/tab_bar_me_selected.png"
      }
    ]
  },