I don't know what your chat program looks like but here's an example for you to try out.

Start a new standard EXE application. Add a RichTextBox to the form. Put an ordinary TextBox under it and add a command button.

You type a line of text in the ordinary TextBox and hit the CommandButton. The text you have typed is then added to the RTF-box.

Put the following code in the Click event of the CommandButton:
Code:
Private Sub Command1_Click()
    Randomize
    With RichTextBox1
        .SelStart = Len(.Text)
        .SelColor = QBColor(Int(Rnd * 16))
        .SelText = Text1.Text & vbCrLf
        Text1 = ""
        Text1.SetFocus
    End With
End Sub
Play around with it for a while.
Good luck!