Colors in a rich text box

[PRIVATE1]

I have a chat application I made in VB . The main window is a richtextbox . I want to add color to the "Nick" the person is using and I tried this

Public Sub colorize()
    Dim posEnd, posStart, x, i As Integer
    
    x = 0
    i = 0

    For i = 0 To Len(RichTextBox1.Text)
        RichTextBox1.SelStart = i
        RichTextBox1.SelLength = 1

        If RichTextBox1.SelText = ">" Then  'start tag
            posStart = i
            RichTextBox1.SelColor = vbRed
        
        End If

    Next i

End Sub

The Probem with that is that evertime something new is put in the box it scrolls through the whole RTB contents and it looks ugly . How do they do it in Mirc ? Should I write all the chat strings to a file and reload it evertime something new is entered ? Any ideas would be great ! Thanks again .