I use this in a semaphore type of application, changing the color of the first ellipse with triggers.

 

                <Viewbox >
                        <Grid Height="50" Width="50" Margin="5" ToolTip="SOF" >  
                        <Grid Margin="0">
                            <Ellipse Fill="Red">
                            <Ellipse.Stroke>
                                    <LinearGradientBrush StartPoint="0.5,0"
                                                         EndPoint="0.5,1"
                                                         ColorInterpolationMode="ScRgbLinearInterpolation">
                                        <GradientStop Color="Black"
                                                      Offset="0" />
                                        <GradientStop Color="Silver"
                                                      Offset="1" />
                                    </LinearGradientBrush>
                                </Ellipse.Stroke>
                            </Ellipse>
                            <Ellipse Margin="1">
                                <Ellipse.Stroke>
                                    <RadialGradientBrush Opacity="0.8"
                                                         ColorInterpolationMode="ScRgbLinearInterpolation">
                                        <GradientStop Offset="0.85"
                                                      Color="Transparent" />
                                        <GradientStop Offset="1"
                                                      Color="Black" />
                                    </RadialGradientBrush>
                                </Ellipse.Stroke>
                                <Ellipse.Fill>
                                    <RadialGradientBrush  Opacity="0.6"
                                                          GradientOrigin="0.5,1.2"
                                                          ColorInterpolationMode="ScRgbLinearInterpolation">
                                        <GradientStop Offset="1"
                                                      Color="#00000000" />
                                        <GradientStop Offset="0.4"
                                                      Color="White" />
                                    </RadialGradientBrush>
                                </Ellipse.Fill>
                            </Ellipse>
                            <Ellipse Margin="1.5"
                                     RenderTransformOrigin="0.5,0">
                                <Ellipse.RenderTransform>
                                    <ScaleTransform ScaleY="0.4"
                                                    ScaleX="0.7" />
                                </Ellipse.RenderTransform>
                                <Ellipse.Fill>
                                    <LinearGradientBrush Opacity="0.85"
                                                         StartPoint="0.5,0"
                                                         EndPoint="0.5,1"
                                                         ColorInterpolationMode="ScRgbLinearInterpolation">
                                        <GradientStop Color="White"
                                                      Offset="0.3" />
                                        <GradientStop Color="Transparent"
                                                      Offset="1" />
                                    </LinearGradientBrush>
                                </Ellipse.Fill>
                            </Ellipse>
                        </Grid>
                        <TextBlock TextWrapping="NoWrap"
                                   Opacity=".75"
                                   FontWeight="Bold"
                                   TextAlignment="Center"
                                   HorizontalAlignment="Center"
                                   VerticalAlignment="Center"
                                   Text="SOF"
                                   TextBlock.FontSize="15"
                                   Margin="2,0,0,0" />
                        </Grid>
                </Viewbox>