B4J Question initializing a RadioButton resets the form BackColor ?

Sub Process_Globals
    Private fx As JFX
    Private MainForm As Form
    Private rb As RadioButton
End Sub

Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    MainForm.Show
    CSSUtils.SetBackgroundColor(MainForm.RootPane,fx.Colors.Yellow)
    rb.Initialize("rb")
    MainForm.RootPane.AddNode(rb,0,0,30,30)
End Sub

MainForm.BackColor=fx.Colors.Yellow

CSSUtils.SetBackgroundColor(MainForm.RootPane,fx.Colors.Yellow)

Sub Process_Globals
    Private MainForm As Form
    Private xui As XUI
    Private rb As RadioButton
End Sub


Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    MainForm.Show
    Dim root As B4XView = MainForm.RootPane
    root.Color = xui.Color_Yellow
    rb.Initialize("rb")
End Sub