call sub to change USERname color - vb.net

Question

I want to change USERname color inside RitchTextBox, I am using this code below to call the SUB but all the text now in red?
UPDATE
Sub AddMessage(txtUsername As String, txtSend As String)
box.SelectionColor = Color.Red
box.AppendText(vbCrLf & txtUsername & "$ ")
box.SelectionColor = Color.Black
box.AppendText(txtSend)
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmdSend.Click
' Shell("net send " & txtcomputer.Text & " " & txtmessage.Text)
Try
If txtPCIPadd.Text = "" Or txtUsername.Text = "" Or txtSend.Text = "" Then
MsgBox("wright a message!", "MsgBox")
Else
client = New TcpClient(txtPCIPadd.Text, 44444)
Dim writer As New StreamWriter(client.GetStream())
txttempmsg.Text = (txtSend.Text)
writer.Write(txtUsername.Text + " # " + txtSend.Text)
AddMessage(txtUsername.Text, txttempmsg.Text + vbCrLf)
'txtmsg.Text="You:" + txtmessage.Text)
writer.Flush()
txtSend.Text = ""
End If
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub

Answer 1

When you have a problem trying to get something to work in your program. It is easier to create a test example that you can then use to figure out what is happening without dealing with a lot of other variables in your larger program. In your case I created a VB Winforms app, added a RichTextBox, two TextBox's and a Button. By doing so I am able to show that the function is working.
Public Class Form1
Sub AddMessage(txtUsername As String, txtSend As String)
box.SelectionColor = Color.Red
box.AppendText(vbCrLf & txtUsername & " :") 'Note added colon
box.SelectionColor = Color.Black
box.AppendText(txtSend) 'Note changed variable name to parameter name
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
AddMessage(txtUsername.Text, txttempmsg.Text)
End Sub
End Class
Example: