We can define different values depending on the platform that the application is executed.
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="App1.Page1">
<ContentPage.Resources>
<ResourceDictionary>
<OnPlatform x:Key="backgroundColor"
x:TypeArguments="Color"
Android="#404040" />
<OnPlatform x:Key="textColor"
x:TypeArguments="Color"
Android="White"
WinPhone="Blue" />
</ResourceDictionary>
</ContentPage.Resources>
<Label x:Name="MyLabel"
Text="Hello World!"
TextColor="{StaticResource Key=textColor}"
BackgroundColor="{StaticResource Key=backgroundColor}" />
</ContentPage>