bon j'ai la solution, j'espere que quelqu'un le serve un jour,
da09.Fill(dst09, "tb_rdv")
Grille.DataSource = dst09.Tables("tb_rdv")
Dim myPane As GraphPane = Zg1.GraphPane
myPane.Title.Text = "Statistique des RDV par TA"
myPane.XAxis.Title.Text = "TA"
myPane.YAxis.Title.Text = "Nombre RDV"
Dim list As New PointPairList()
'Dim rand As New Random()
Dim n As Integer = dst09.Tables("tb_rdv").Rows.Count
Dim i As Integer
For i = 0 To n - 1
'rand.NextDouble() * 1000
Dim x As Double = CDbl(Grille.Item(i, 0)) 'code TA
Dim y As Double = CDbl(Grille.Item(i, 2)) 'nombre total des RDV
Dim z As Double = i / 4.0
list.Add(x, y, z)
Next
Dim myCurve As BarItem = myPane.AddBar("couleur de TA", list, Color.Blue)
Dim colors As Color() = {Color.Red, Color.Yellow, Color.Green, Color.Blue, Color.Purple}
myCurve.Bar.Fill = New Fill(colors)
myCurve.Bar.Fill.Type = FillType.GradientByZ
myCurve.Bar.Fill.RangeMin = 0
myCurve.Bar.Fill.RangeMax = 4
myPane.Chart.Fill = New Fill(Color.White, Color.FromArgb(220, 220, 255), 45)
myPane.Fill = New Fill(Color.White, Color.FromArgb(255, 255, 225), 45)
' Tell ZedGraph to calculate the axis ranges
Zg1.AxisChange()
Zg1.Refresh()
Zg1.Visible = True
Call deconnection()
voir ce lien qui m'aider : http://zedgraph.org/wiki/index.php?title=Multi-Colored_Bar_Demo