A year old question, but here we go.
If you have your series defined in your XAML, just set the attribute Stroke="Blue"
If you're creating your series dynamically, add a property MySeriesStroke
and bind it to your series
Private _mySeriesStroke As Brush
Public Property MySeriesStroke As Brush
Get
Return _mySeriesStroke
End Get
Set(ByVal value As Brush)
If _mySeriesStroke IsNot value Then
_mySeriesStroke = value
raisePropertyChangeEvent("MySeriesStroke")
End If
End Set
End Property
...
Sub AddSeries()
...
MySeries.SetBinding(LineSeries.StrokeProperty, "MySeriesStroke")
...
End Sub
...
Sub ChangeStroke(ByRef brush As Brush)
MySeriesStroke = brush
End Sub
If you post your code, I can answer more to your op.