<Grid x:Name="LayoutRoot" Background="White"> <Grid.Resources> <esri:SimpleFillSymbol x:Key="DefaultFillSymbol" Fill="#33FF0000" BorderBrush="Red" BorderThickness="2" /> </Grid.Resources> .....
MyDrawObject = new Draw(MyMap)
{
FillSymbol = LayoutRoot.Resources["DefaultFillSymbol"] as ESRI.ArcGIS.Client.Symbols.FillSymbol,
.......