Every class that derives from VisualElement has a Resource property of type ResourceDictionary which can be used in order common values for different object properties.
<?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>
<Color x:Key="textColor">Blue</Color>
<Color x:Key="backgroundColor" x:FactoryMethod="FromHsla">
<x:Arguments>
<x:Double>0</x:Double>
<x:Double>1</x:Double>
<x:Double>0.5</x:Double>
<x:Double>1</x:Double>
</x:Arguments>
</Color>
<x:Double x:Key="rotation">45</x:Double>
</ResourceDictionary>
</ContentPage.Resources>
<Label x:Name="MyLabel"
Text="Hello World!"
TextColor="{StaticResource Key=textColor}"
BackgroundColor="{StaticResource Key=backgroundColor}"
Rotation="{StaticResource Key=rotation}" />
</ContentPage>