title: remove back color from multiple positions in richTextBox
body: <p>I have a rich text box and I've implemented a search option for it. When the user searches a string, all the matches gets highlighted with yellow background. I want that when the user presses the search button again, all of the previous highlights will be removed before the new search begins.</p>
  
  <p>I found out two ways to do it:
  1. select all text and then choose the back color to be the default one.
  2. remove all text from the text box and then put it back again.</p>
  
  <p>Both ways work, but it doesn't look natural when I use them.
  So, is there another way that I can remove all highlights from the text?</p>
  
  <p>I'm using .NET framework 4 and I write in C#.</p>