A quick and easy way to make sure every activity has the same background color, is to create a theme for your activities to use. That theme would specify the android:windowBackground.
First define the color in values/colors.xml
<resources>
<color name="background">#FF0000 </color>
</resources>
Create a themes.xml file in res/values that references that color:
<resources>
<style name="MyTheme" parent="@android:style/Theme.Light">
<item name="android:windowBackground">@color/background</item>
</style>
</resources>
... and then in your AndroidManifest.xml specify this as the theme for your activities to use.
<activity
android:name=".MyActivity"
android:theme="@style/MyTheme" />
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