What is the default layout background

You can use your theme's default background color by referencing:

?android:colorBackground

Go to Manifest

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/MyMaterialTheme.NoActionBar">

You see the Theme is MyMaterialTheme.NoActionBar

So go to res -> values -> styles

So for me the default is #FFFAFAFA

When i put the suggested colors #EEEEEE or #FAFAFA, it worked on some phones, and on other phones it was off, so that's what I found with trial and error

The default background color for light theme is: #EEEEEE

Is almost white, but not completely.

It worked for me, hope its work for you.

UPDATE: In new versions you could be looking for #FAFAFA

To change your background (if this is in fact what you are looking to do):

in styles.xml

<style name = "MyDefaultStyle" parent = "@android:style/Theme">
    <item name = "android:windowBackground">@drawable/default_drawable_bg</item>
</style>

and in your manifest

<application
    android:name="MyApp"
    android:theme="@style/MyDefaultStyle" >