Entry appearing black or gray on some Android phones?

In my Xamarin Forms app I defined an Entry like this:

<Entry Placeholder="Type Email"
        Text="{Binding Email, Mode=TwoWay}"
        Keyboard="Email"
        BackgroundColor="{x:Static Color.White}"
        Opacity="1"
        TextColor="{x:Static Color.Black}" />

On my device and the Android emulator, it has a white background and black text. Yet on Samsung android phones like the Note 2 or the Samsung s5 the entry shows up with a black or gray background. Any suggestions why that is happening or what I can do about it?