algo asi:
saludos.
Código (vbnet) [Seleccionar]
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
For i As Integer = 1 To 500
RichTextBox1.Text += "Linea " & i & vbNewLine
Next
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
For i As Integer = 0 To RichTextBox1.Lines.Length - 1
Dim first As Integer = RichTextBox1.GetFirstCharIndexFromLine(i)
RichTextBox1.Select(first, RichTextBox1.Lines(i).Length)
RichTextBox1.SelectionBackColor = If((i Mod 2 = 0), Color.Red, Color.White)
RichTextBox1.SelectionColor = If((i Mod 2 = 0), Color.Black, Color.Green)
Next
End Sub
End Class
saludos.