How to change the default fillcolor of Amos 18

It really bothers me that the color inAmos 17 and 18 use the color which is very ugly.
I search in Amos Help document and findthe following:
Imports AmosGraphics
Imports System.drawing

Public Class CustomCode
Implements IPlugin

Public Function Mainsub() As Integer ImplementsIPlugin.Mainsub
Dim x As PDElement
PathDiagrammer.UndoToHere()
On Error Goto ErrExit
For Each x In PathDiagrammer.PDElements
If x.IsLatentVariable Then
x.Undraw()
x.BorderColor = Color.Black.ToArgb
x.FillColor =Color.White.ToArgb
x.NameColor = Color.Red.ToArgb
x.ParameterColor = Color.Green.ToArgb
x.Fillstyle = 0
x.Penwidth = 2
x.Draw()
End If
Next
ErrExit:
PathDiagrammer.UndoResume()
End Function

Public Function Name() As String ImplementsIPlugin.Name
End Function

Public Function Description() As String ImplementsIPlugin.Description
End Function
End Class
this reminds me to write syntax to calculatein Amos.