RichTextBox flikers when syntax highlight - vb.net

Question

I am writing an IDE an while working on syntax highlighting, i've encountered a very annoying issue.
When I type something, the text flickers...
Here is my code:
Dim KeyWords As List(Of String) = New List(Of String)(New String() {"void", "int", "long", "char", "short", "unsigned", "signed", "#include", "#define", "return"})
Dim KeyWordsColors As List(Of Color) = New List(Of Color)(New Color() {Color.Purple, Color.Purple, Color.Purple, Color.Purple, Color.Purple, Color.Purple, Color.Purple, Color.Olive, Color.Olive, Color.Blue})
Private Sub RichTextBox1_TextChanged(sender As Object, e As EventArgs) Handles RichTextBox1.TextChanged
Dim words As IEnumerable(Of String) = RichTextBox1.Text.Split(New Char() {" "c, ".", ",", "?", "!", "(", Chr(13), Chr(10), " "})
Dim index As Integer = 0
Dim rtb As RichTextBox = sender 'to give normal color according to the base fore color
For Each word As String In words
'If the list contains the word, then color it specially. Else, color it normally
'Edit: Trim() is added such that it may guarantee the empty space after word does not cause error
coloringRTB(sender, index, word.Length, If(KeyWords.Contains(word.ToLower().Trim()) Or KeyWords.Contains("<"), KeyWordsColors(KeyWords.IndexOf(word.ToLower().Trim())), rtb.ForeColor))
index = index + word.Length + 1 '1 is for the whitespace, though Trimmed, original word.Length is still used to advance
Next
Dim strings() As String = RichTextBox1.Text.Split(Chr(34))
Dim count As Integer = 0
Dim cpart As Integer = 0
For Each part In strings
cpart = cpart + 1
If cpart Mod 2 = 0 Then
coloringRTB(RichTextBox1, count - 1, part.Length + 2, Color.Olive)
End If
count = count + part.Length + 1
Next
Dim strings2() As String = RichTextBox1.Text.Split(New Char() {"<", ">"})
count = 0
cpart = 0
For Each part In strings2
cpart = cpart + 1
If cpart Mod 2 = 0 Then
coloringRTB(RichTextBox1, count - 1, part.Length + 2, Color.Olive)
End If
count = count + part.Length + 1
Next
End Sub
Private Sub coloringRTB(rtb As RichTextBox, index As Integer, length As Integer, color As Color)
Dim selectionStartSave As Integer = rtb.SelectionStart 'to return this back to its original position
rtb.SelectionStart = index
rtb.SelectionLength = length
rtb.SelectionColor = color
rtb.SelectionLength = 0
rtb.SelectionStart = selectionStartSave
rtb.SelectionColor = rtb.ForeColor 'return back to the original color
End Sub
Private Sub RichTextBox1_KeyUp(sender As Object, e As KeyPressEventArgs) Handles RichTextBox1.KeyPress
If e.KeyChar = "{"c Then
RichTextBox1.SelectedText = "{}"
RichTextBox1.SelectionStart = RichTextBox1.Text.Substring(0, RichTextBox1.SelectionStart).LastIndexOf("{") + 1
e.Handled = True
End If
If e.KeyChar = "("c Then
RichTextBox1.SelectedText = "()"
RichTextBox1.SelectionStart = RichTextBox1.Text.Substring(0, RichTextBox1.SelectionStart).LastIndexOf("(") + 1
e.Handled = True
End If
If e.KeyChar = "["c Then
RichTextBox1.SelectedText = "[]"
RichTextBox1.SelectionStart = RichTextBox1.Text.Substring(0, RichTextBox1.SelectionStart).LastIndexOf("[") + 1
e.Handled = True
End If
If e.KeyChar = "'"c Then
RichTextBox1.SelectedText = "''"
RichTextBox1.SelectionStart = RichTextBox1.Text.Substring(0, RichTextBox1.SelectionStart).LastIndexOf("'")
e.Handled = True
End If
Dim currentLength = RichTextBox1.Text.Length
End Sub
hope someone can help Thanks ^_^
RichTextBox1 is the richtextbox