HarmonyOS flutter app启动目前是白色背景，是否可自定义样式？

"abilities": [  
{  
  "name": "EntryAbility",  
"srcEntry": "./ets/entryability/EntryAbility.ets",  
"description": "$string:EntryAbility_desc",  
"icon": "$media:ic_eshop",  
"label": "$string:EntryAbility_label",  
"startWindowIcon": "$media:ic_eshop",  
"startWindowBackground": "$color:start_window_background",  
"exported": true,  
"skills": [  
  {  
    "entities": [  
    "entity.system.home"  
    ],  
    "actions": [  
    "action.system.home"  
    ]  
  }  
  ]  
}  
]

"startWindowBackground": "$color:start_window_background"

"icon": "$media:ic_eshop"

@Builder  
componentBuilder() {  
  // 自定义加载界面的样式  
  Column() {  
    Text("Loading...")  
  }  
}