How can I define and use a variable in XAML to define a color?

Question

I have a number of elements in my XAML which define Foreground="#555" to be the color of faded text in a readonly textbox.

<TextBlock Text="{Binding SingularModelClassFileTitle}" Margin="0 10 0 0"/>
<TextBox Text="{Binding SingularModelClassFileName}"
         HorizontalAlignment="Left"
         IsReadOnly="True"
         Foreground="#555"
         Width="500"/>
<TextBox 
 VerticalScrollBarVisibility="Visible"
 AcceptsReturn="True"                  
 Width="500" 
 Height="100" 
 IsReadOnly="True" 
 Foreground="#555"
 Text="{Binding SingularModelClassContent}"
 HorizontalAlignment="Left"
 Margin="0 0 0 20"/>

How can I put this value in a XAML variable and reference in each attribute it so that I only have to change it in one place?

I'm thinking you can do something like this:

<sys:String x:Key="ReadOnlyTextColor">#555</sys:String>

...

    <TextBox Foreground="{StaticResource ReadOnlyTextColor}"/>

And what would be the property xmlns:sys=... reference for this?

Answer 1

Try defining your color as a SolidColorBrush:

<SolidColorBrush x:Key="ReadOnlyTextBrush" Color="#555555" />

...

<TextBox Foreground="{StaticResource ReadOnlyTextColor}" />

Answer 2

Sometimes you may need to define colors rather than brushes : (one case you would want this is to be able to define Gradients with color parameters) In that case you could just define them like this:

 <Color x:Key="ButtonColor1">Blue</Color>
 <Color x:Key="ButtonColor1">#AABBCC</Color>
 <Color x:Key="ButtonColor1" A="00" R="124" G="111" B="44"/>