Selectively coloring text in RichTextBox

Question

How can I paint in red every time I meet the letter \"A\" in RichTextBox?

Answer 1

This is the C# code for EJ Brennan's answer:

public string Highlight(object Search_Str, string InputTxt, string StartTag, string EndTag) 
{
    return Regex.Replace(InputTxt, "(" + Regex.Escape(Search_Str) + ")", StartTag + "$1" + EndTag, RegexOptions.IgnoreCase);
}