Public Property FillColor1 As Brush

public Brush FillColor1 {get; set;}

<!-- Standard SolidColorBrush example -->
   <esri:ScaleBar Name="ScaleBar1" Map="{Binding ElementName=Map1}" FillColor1="Magenta" 
   FillColor2="Yellow" />
   
   <!-- Alternative LinearGradientBrush and RadialGradientBrush example -->        
   <esri:ScaleBar Name="ScaleBar2" Map="{Binding ElementName=Map1}"
          HorizontalAlignment="Left" VerticalAlignment="Top"  
          MapUnit="DecimalDegrees" DisplayUnit="Miles"  
          BarHeight="30" TargetWidth="400" 
          TextColor="Black" FontFamily="Courier New" FontSize="18" >
     <esri:ScaleBar.FillColor1>
       <LinearGradientBrush StartPoint="0,0" EndPoint="1,1">
           <GradientStop Color="Yellow" Offset="0.0" />
           <GradientStop Color="Black" Offset="1.0" />
       </LinearGradientBrush>
     </esri:ScaleBar.FillColor1>
     <esri:ScaleBar.FillColor2>
       <RadialGradientBrush GradientOrigin="0.5,0.5" Center="0.5,0.5" RadiusX="0.5" RadiusY="0.5">
           <GradientStop Color="Yellow" Offset="0" />
           <GradientStop Color="Black" Offset="1.0" />
       </RadialGradientBrush>
     </esri:ScaleBar.FillColor2>
   </esri:ScaleBar>

//The ScaleBar1 and ScaleBar2 were define previously in the code...
            
//Standard SolidColorBrush example
System.Windows.Media.Color myFillColor1a = Color.FromArgb(255, 255, 255, 0); //Yellow
ScaleBar1.FillColor1 = new System.Windows.Media.SolidColorBrush(myFillColor1a);
System.Windows.Media.Color myFillColor2a = Color.FromArgb(255, 0, 0, 0); //Black
ScaleBar1.FillColor2 = new System.Windows.Media.SolidColorBrush(myFillColor2a);
            
            
//Alternative LinearGradientBrush and RadialGradientBrush example
System.Windows.Media.GradientStopCollection myGradientStopCollection = new System.Windows.Media.GradientStopCollection();
LinearGradientBrush myLinearGradientBrush = new LinearGradientBrush();
            
GradientStop gradientStop1 = new GradientStop();
System.Windows.Media.Color myFillColor1b = Color.FromArgb(255, 255, 255, 0); //Yellow
gradientStop1.Color = myFillColor1b;
            
GradientStop gradientStop2 = new GradientStop();
System.Windows.Media.Color myFillColor2b = Color.FromArgb(255, 0, 0, 0); //Black
gradientStop2.Color = myFillColor2b;
gradientStop2.Offset = 1;
            
myGradientStopCollection.Add(gradientStop1);
myGradientStopCollection.Add(gradientStop2);
            
ScaleBar2.FillColor1 = new System.Windows.Media.LinearGradientBrush(myGradientStopCollection, 45);
ScaleBar2.FillColor2 = new System.Windows.Media.RadialGradientBrush(myFillColor1b, myFillColor2b);

'The ScaleBar1 and ScaleBar2 were define previously in the code...
            
'Standard SolidColorBrush example
Dim myFillColor1a As System.Windows.Media.Color = Color.FromArgb(255, 255, 255, 0) 'Yellow
ScaleBar1.FillColor1 = New System.Windows.Media.SolidColorBrush(myFillColor1a)
Dim myFillColor2a As System.Windows.Media.Color = Color.FromArgb(255, 0, 0, 0) 'Black
ScaleBar1.FillColor2 = New System.Windows.Media.SolidColorBrush(myFillColor2a)
            
            
'Alternative LinearGradientBrush and RadialGradientBrush example
Dim myGradientStopCollection As System.Windows.Media.GradientStopCollection = New System.Windows.Media.GradientStopCollection
Dim myLinearGradientBrush As LinearGradientBrush = New LinearGradientBrush()
            
Dim gradientStop1 As GradientStop = New GradientStop()
Dim myFillColor1b As System.Windows.Media.Color = Color.FromArgb(255, 255, 255, 0) 'Yellow
gradientStop1.Color = myFillColor1b
            
Dim gradientStop2 As GradientStop = New GradientStop()
Dim myFillColor2b As System.Windows.Media.Color = Color.FromArgb(255, 0, 0, 0) 'Black
gradientStop2.Color = myFillColor2b
gradientStop2.Offset = 1
            
myGradientStopCollection.Add(gradientStop1)
myGradientStopCollection.Add(gradientStop2)
            
ScaleBar2.FillColor1 = New System.Windows.Media.LinearGradientBrush(myGradientStopCollection, 45)
ScaleBar2.FillColor2 = New System.Windows.Media.RadialGradientBrush(myFillColor1b, myFillColor2b)