This approach worked for me! Thanks
Can you help please, why this decision doesn't work for myMeasureAction.MeasureMode = MeasureAction.Mode.Radius? Procedure Graphics_CollectionChanged is never started...
This is a very old post but in case some else needs...change color similar manner as this...
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<esri:MeasureAction AreaUnit="SquareFeet" DisplayTotals="True" DistanceUnit="Feet" MapUnits="Meters"
TargetName="myMap"
MeasureMode="Polyline" FillSymbol="{StaticResource defaultFillSymbol}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
<UserControl.Resources>
<esri:SimpleFillSymbol x:Key="DefaultFillSymbol" Fill="#33FF0000" BorderBrush="Red" BorderThickness="2" />
</UserControl.Resources>