Regardless of the RadEntry's BackgroundColor property, I've noticed the visible-background-color to differ when the RadEntry receives active focus.
The observed behavior is this:
Typically, in day mode settings (Windows default), the RadEntry's BackgroundColor == white so you don't see the problem. However, in night mode settings (Android default), we want the RadEntry's BackgroundColor == black so the problem is more prevalent since you're typing white text on a white background.
When using Visual States, and, if you try to re-enforce the same BackgroundColor property in all of the visual states, sometimes focus, hover, unfocus, hover, focus sequence will allow you to edit in the RadEntry in your desired RadEntry's BackgroundColor property instead of white, but, most of the time is white.
This problem can be reproduced on Windows and Android if you set your application to night mode Application.Current.UserAppTheme = AppTheme.Dark and set RadEntry's BackgroundColor=Black and TextColor=White in XAML. Put 2 or 3 RadEntry's on the page so you can navigate between them to see the problem.