Set background white to splash screen for Android

Hello, I need to know, how can I set the background to splash screen?, because when I set the splash screen on the settings into unity. My Splash Screen is white, but in some devices the splash screen is with border left and right black because the application background seems to be black.

I did try to set this property android:theme into the AndroidManifest but it seems not work.

 <activity android:name="com.unity3d.player.UnityPlayerNativeActivity" android:label="@string/app_name" android:theme="@style/HH.Background">

I attached image with the file style what I did put on the project. That file is to configure the HH.Background. That is the code.

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <color name="background_color">#FFFFFF</color>
     <style name="HH.Background" parent="@android:style/Theme">
         <item name="android:windowNoTitle"> true</item>
         <item name="android:windowFullscreen">true</item>
         <item name="android:windowBackground">@color/background_color</item>
     </style> 
 </resources>

If someone knows the solution I appreciate so much his help.

Thanks a Lot.