vb 如何在程序运行过程中改变 richtextbox中字体的大小和颜色

Private Sub Command1_Click() '改变颜色和字体、大小
With RichTextBox1
    .SelStart = 0
    .SelLength = 3
    .SelColor = RGB(255, 0, 0)
    .SelFontSize = 35
    .SelStart = 3
    .SelFontSize = 10
    .SelStart = 6
    .SelLength = 3
    .SelColor = RGB(0, 255, 0)
    .SelFontName = "楷体_GB2312"
    .SelFontSize = 20
End With
End Sub

Private Sub Form_Load()
RichTextBox1.Text = "红色大黑色小绿色楷"
End Sub