RichTextBox1.SelectionStart = RichTextBox1.Find("Palabra")
RichTextBox1.SelectionColor = Color.Yellow ' El color que quieras

Public Class Form1
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        If RichTextBox1.Text = "" Then
            MessageBox.Show("No se puede compilar un texto vacio")
            Return
        End If
        If SaveFileDialog1.ShowDialog = DialogResult.OK Then
            RichTextBox1.SaveFile(SaveFileDialog1.FileName, RichTextBoxStreamType.PlainText)
            ProgressBar1.Visible = True
            Timer1.Start()
        End If
        Form1.ActiveForm().Text() = "Batch Creator" + SaveFileDialog1.FileName
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If OpenFileDialog1.ShowDialog = DialogResult.OK Then
            RichTextBox1.LoadFile(OpenFileDialog1.FileName, RichTextBoxStreamType.PlainText)
        End If
        Form1.ActiveForm().Text() = "Batch Creator" + OpenFileDialog1.FileName
    End Sub
 
    Private Sub SaveFileDialog1_FileOk(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles SaveFileDialog1.FileOk
End Sub
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        ProgressBar1.Increment(10)
        If ProgressBar1.Value = ProgressBar1.Maximum Then
            Timer1.Stop()
            MessageBox.Show("Se ha creado satisfactoriamente el archivo .bat en la direccion especificada")
            ProgressBar1.Value = ProgressBar1.Minimum
            ProgressBar1.Visible = False
            Return
        End If
    End Sub
 
    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        If RichTextBox1.Text = "" Then
            MessageBox.Show("Ya hay un nuevo documento abierto")
            Return
        End If
        Form2.Show()
    End Sub
 
    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        Form3.SHOW()
    End Sub
 
    Private Sub RichTextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RichTextBox1.TextChanged
 
    End Sub
 
End Class

Private Sub RichTextBox1_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles RichTextBox1.LostFocus
 
RichTextBox1.Find("@")
RichTextBox1.SelectionColor = Color.Red
 
End Sub