Código
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.