'searches teh text and colors it...
    Private Sub ExtendedRichTextBox_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ExtendedRichTextBox.TextChanged

        Dim selectionAt As Integer = ExtendedRichTextBox.SelectionStart

        'find out the linenumber...
        lineNumber = ExtendedRichTextBox.GetLineFromCharIndex(ExtendedRichTextBox.SelectionStart()) + 1

        If ExtendedRichTextBox.GetFirstCharIndexFromLine(lineNumber) = -1 Then
            line = ExtendedRichTextBox.Text.Substring(ExtendedRichTextBox.GetFirstCharIndexOfCurrentLine())
            startCharIndex = 0
        Else
            line = ExtendedRichTextBox.Text.Substring(startCharIndex, ExtendedRichTextBox.GetFirstCharIndexFromLine(lineNumber) - ExtendedRichTextBox.GetFirstCharIndexOfCurrentLine)
        End If

        'regular expression...
        Dim reg_exp As Regex

        'give reg_exp some values...
        For i As Integer = 0 To 4

            'give reg_exp a value from the array...
            reg_exp = New Regex(syntaxText(i))

            'search for matches...
            Dim match As Match
            match = reg_exp.Match(line)

            'give the match the right color...
            If reg_exp.IsMatch(line) Then

                With ExtendedRichTextBox
                    .Select(match.Index, match.Length)
                    .SelectionColor = syntaxColor(i)
                    .SelectionStart = selectionAt
                    .SelectionColor = textColor
                End With

            End If
        Next

    End Sub

Imports System.TextImports System.Text.RegularExpressionsPublic Class Form1    Dim textColor As Color = Color.Black    Dim syntaxColor As Color = Color.Blue    Dim keywords() As String = {"apple", "orange", "grape", "pear", "banana"}    ' this is used to prevent the flickering from all the selecting and deselecting    Declare Function LockWindowUpdate Lib "user32" (ByVal hwndLock As Integer) As Integer    Private Sub RichTextBox1_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles RichTextBox1.TextChanged        LockWindowUpdate(RichTextBox1.Handle)        Dim selectionStart As Integer = RichTextBox1.SelectionStart ' stores the caret position        Dim firstCharIndex = RichTextBox1.GetFirstCharIndexOfCurrentLine()        Dim lineNumber As Integer = RichTextBox1.GetLineFromCharIndex(firstCharIndex)        Dim currentLine As String = RichTextBox1.Lines(lineNumber)        ' first, make sure that the entire line is set to the text color        RichTextBox1.Select(firstCharIndex, currentLine.Length)        RichTextBox1.SelectionColor = textColor        ' build a regular expression string that contains all the keywords        Dim builder As StringBuilder = New StringBuilder()        For i As Integer = 0 To keywords.Length - 1            If i > 0 Then                builder.Append("|")            End If            builder.Append("\b" + keywords(i) + "\b")        Next        ' get each of the matches and set the text color to the syntaxColor value        Dim matches As MatchCollection = Regex.Matches(currentLine, builder.ToString(), RegexOptions.IgnoreCase)        For i As Integer = 0 To matches.Count - 1            With RichTextBox1                .Select(firstCharIndex + matches(i).Index, matches(i).Length)                .SelectionColor = syntaxColor                .SelectionStart = firstCharIndex + matches(i).Index + matches(i).Length                .SelectionColor = textColor            End With        Next        ' set the caret back to its starting position        RichTextBox1.SelectionStart = selectionStart        LockWindowUpdate(0)    End SubEnd Class