public abstract class SankeyColorizerBase :
    DependencyObject,
    INotifyPropertyChanged

Public MustInherit Class SankeyColorizerBase
    Inherits DependencyObject
    Implements INotifyPropertyChanged

<dxsa:SankeyDiagramControl.Colorizer>
    <local:MyColorizer LinkSourceColor="Yellow" LinkTargetColor="Red" />
</dxsa:SankeyDiagramControl.Colorizer>

public class MyColorizer : SankeyColorizerBase {
    readonly Random rand = new Random();
    readonly Dictionary<string, Color> KeyColorPairs = new Dictionary<string, Color>();
    public Color LinkSourceColor { get; set; }
    public Color LinkTargetColor { get; set; }
    public override Color GetLinkSourceColor(SankeyLink link) {
        return LinkSourceColor;
    }
    public override Color GetLinkTargetColor(SankeyLink link) {
        return LinkTargetColor;
    }
    public override Color GetNodeColor(SankeyNode info) {
        if (!KeyColorPairs.TryGetValue((string)info.Tag, out Color nodeColor)) {
            nodeColor = GenerateColor();
            KeyColorPairs.Add((string)info.Tag, nodeColor);
        }
        return nodeColor;
    }
    private Color GenerateColor() {
        return Color.FromRgb((byte)rand.Next(256), (byte)rand.Next(256), (byte)rand.Next(256));
    }
}

Public Class MyColorizer
    Inherits SankeyColorizerBase
    Private ReadOnly rand As Random = New Random()
    Private ReadOnly KeyColorPairs As Dictionary(Of String, Color) = New Dictionary(Of String, Color)()
    Public Property LinkSourceColor As Color
    Public Property LinkTargetColor As Color

    Public Overrides Function GetLinkSourceColor(ByVal link As SankeyLink) As Color
        Return LinkSourceColor
    End Function

    Public Overrides Function GetLinkTargetColor(ByVal link As SankeyLink) As Color
        Return LinkTargetColor
    End Function

    Public Overrides Function GetNodeColor(ByVal info As SankeyNode) As Color
        Dim nodeColor As Color = Nothing

        If Not KeyColorPairs.TryGetValue(CStr(info.Tag), nodeColor) Then
            nodeColor = GenerateColor()
            KeyColorPairs.Add(CStr(info.Tag), nodeColor)
        End If

        Return nodeColor
    End Function

    Private Function GenerateColor() As Color
        Return Color.FromRgb(rand.Next(256), rand.Next(256), rand.Next(256))
    End Function
End Class