Sorry for not posting sooner I've been in meetings this morning and not had chance to update the thread.

 I found that the lines were getting painted in black while attempting to paint new points on the chart not in the colour of the series... The code I've got now to do almost what I need the UltraChart looks like this (note that the points now paint in the correct colour after digging through some more properties). To be honest I am actually trying to use the custom interpolation but it is going a little pear shaped and has been for a week now :|

Private Sub ulchtRender_FillSceneGraph(ByVal sender As Object, ByVal e As Infragistics.UltraChart.Shared.Events.FillSceneGraphEventArgs) Handles ulchtRender.FillSceneGraph

If Me.ulchtRender.ChartType = ChartType.LineChart Then

If (TypeOf p Is Polyline) Then

Dim Chartpoints As ChartPointsToPaint = Nothing

StartPointX = Nothing
StartPointY = Nothing
CurrentPointX = Nothing
CurrentPointY = Nothing

For Each pt As Infragistics.UltraChart.Core.Primitives.DataPoint In CType(p, Infragistics.UltraChart.Core.Primitives.Polyline).points
If pt.Value IsNot Nothing Then

'Points to paint in case there is only 1 point for the series

paintPoint.StartPointX = pt.point.X
paintPoint.StartPointY = pt.point.Y
paintPoint.LineColour = p.PE.Fill
m_PaintPoints.Add(paintPoint)
Next

For Each paintPt As ChartPointsToPaint In m_PaintPoints
Dim myCicrle As New Ellipse(New System.Drawing.Point(CInt(paintPt.StartPointX), CInt(paintPt.StartPointY)), 2)
myCicrle.PE = New PaintElement(paintPt.LineColour, paintPt.LineColour, GradientStyle.Circular)
e.SceneGraph.Add(myCicrle)
Next

m_PaintPoints.Clear()
End If

End Sub

Public Structure ChartPointsToPaint
Public rowID As Integer
Public StartPointX As Object
Public StartPointY As Object
Public EndPointX As Object
Public EndPointY As Object
Public LineColour As Drawing.Color
End Structure

You can try adding:

myCicrle.PE.StrokeWidth = 0

because by default a black line is drawn.

Something slightly off at a tangent; Why if there is only 1 data point for a series does it not plot the point? The whole excercise of the code above was JUST to plot the points so that we could view them on the chart.