Q:

Android - gray background instead of white

Each "layout" I set a white background and "Manifest" I set Theme. Light. 
Still receives a gray background instead of white.  Why? 
Edit:
Manifest.xml
android:theme="@android:style/Theme. Light. NoTitleBar">

Layout
android:background="@android:color/white" 

A:

Theme. Light does not mean that it will be white.  It just means that it will be light, not dark :P This is not theme.white. 
Each device manufacturer can customize Android OS on his phone for example to preferred colors and look & feel.  In particular he can define styles for his Android implementation - Light and dark.  Thanks to that your app may look differently on various devices, however it will always fit the style used on this device (every app in style Theme. Light will have grey background on this device, unless you set android:background="@android:color/white" )
Your device's manufacturer defined style Theme. Light as style with grey background. 
Hope that I am clear - otherwise do not hesitate to ask

