Put this somewhere in the General Declarations area:
Code:
Private Const GWL_STYLE = (-16)
You may get other non-defined things but come on, really...
This is a TreeView! And it requires going to the Components window (OH THE HORROR)!
So nobody really feels like actually trying out this code in VB.

As for the no-popup-window and setting the color directly in the code, replace these subs:
Code:
Private Sub cmdBackColor_Click()
    Dim lngColor As Long
    
    On Error Resume Next
    
    With CommonDialog1
        .CancelError = True
        .ShowColor
        
        If Err.Number = cdlCancel Then Exit Sub
        
        lngColor = .Color
    End With
    
    SetTreeColor TreeView1, BACK_COLOR, lngColor
End Sub


Private Sub cmdForeColor_Click()
    Dim lngColor As Long
    Dim lngStyle As Long
    
    On Error Resume Next
    
    With CommonDialog1
        .CancelError = True
        .ShowColor
        
        If Err.Number = cdlCancel Then Exit Sub
        
        lngColor = .Color
    End With
    SetTreeColor TreeView1, FORE_COLOR, lngColor
End Sub
With these:
Code:
Private Sub cmdBackColor_Click()
    Dim lngColor As Long

    lngColor = RGB(50, 100, 200) ' BackColor
    
    SetTreeColor TreeView1, BACK_COLOR, lngColor
End Sub

Private Sub cmdForeColor_Click()
    Dim lngColor As Long

    lngColor = RGB(200, 100, 50) ' ForeColor

    SetTreeColor TreeView1, FORE_COLOR, lngColor
End Sub