Following example add some custom colors into colordialog using vb.net like this:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim objColorDlg As New System.Windows.Forms.ColorDialog Dim Colors() As Integer = { _ &H88FF, &H99FF, &HBBB, &H999, _ &HCCFF, &HDDFF, &HEEFF, &HEEE} objColorDlg.CustomColors = Colors objColorDlg.Color = Color.Red If objColorDlg.ShowDialog() = DialogResult.OK Then 'Write your Code End If End Sub