C# :: Custom Button Shape (WPF)

I have begun switching from WinForms to WPF and I'm having a hard time understanding the new concepts. In WinForms, I had a few User Controls, custom drawn using shapes (rectangles, ellipses, etc). They had some unique properties, like "Flashing" (setting this property to True and setting the "Flash Interval" property to 500 would have resulted in the control changing its background color to white and back again, every 0.5 seconds), "Beeping", etc.

I have tried to replicate these controls in WPF/XAML and so far managed to draw the shape. However, when it came to implementing a custom property that would redraw the background color of the rectangle every interval set by user in another property, i got stuck. The property is being set, but it doesn't change the background color. Alternatively, i have tried this method, with the same results (i got it to show in the "Properties" window in Visual Studio, i can set it, it is being stored in XAML, but it doesn't affect the background.

C# code behind:
public struct LCARSColors
{
public static Brush DarkBlue = (Brush)(new BrushConverter().ConvertFrom("#FF3366CC"));
public static Brush LightBlue = (Brush)(new BrushConverter().ConvertFrom("#FF99CCFF"));
public static Brush Pink = (Brush)(new BrushConverter().ConvertFrom("#FFCC99CC"));

[Code] ....

If i use this line (commented in this code sample):

<!--<SolidColorBrush x:Name="MySolidColorBrush" Color="{DynamicResource DarkBlue}" />-->

The background is colored in DarkBlue (as defined). But if i use this line:

<SolidColorBrush x:Name="MySolidColorBrush" Color="{Binding BackgroundColor, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />

Nothing happens, the rectangle disappears entirely. If i add this to the above line:

FallbackValue=LightYellow

The rectangle is colored in LightYellow, meaning that the property is not accepted and the fallback value is used. Why?