public class DiagramEdgeEventArgs :
    EventArgs

Public Class DiagramEdgeEventArgs
    Inherits EventArgs

<dx:ASPxDiagram ID="Diagram" runat="server" Width="100%" Height="600px"
    NodeDataSourceID="FlowNodeDemoDataSource" EdgeDataSourceID="FlowEdgeDemoDataSource"
    OnEdgeDataBound="Diagram_EdgeDataBound">
    <Mappings>
        <Node Key="ID" Type="Type" Width="Width" Height="Height" />
        <Edge Key="ID" FromKey="FromID" ToKey="ToID" Text="Text" />
    </Mappings>
</dx:ASPxDiagram>

protected void Diagram_EdgeDataBound(object sender, DevExpress.Web.ASPxDiagram.DiagramEdgeEventArgs e) {
    if (e.Edge.Text == "No") {
        e.Edge.Style = "stroke: red";
        e.Edge.TextStyle = "fill: red";

    }
    if (e.Edge.Text == "Yes") {
        e.Edge.Style = "stroke: green";
        e.Edge.TextStyle = "fill: green";

    }
}

Protected Sub Diagram_EdgeDataBound(ByVal sender As Object, ByVal e As DevExpress.Web.ASPxDiagram.DiagramEdgeEventArgs)
    If e.Edge.Text = "No" Then
        e.Edge.Style = "stroke: red"
        e.Edge.TextStyle = "fill: red"
    End If

    If e.Edge.Text = "Yes" Then
        e.Edge.Style = "stroke: green"
        e.Edge.TextStyle = "fill: green"
    End If
End Sub