Find string and set its color in a RichTextBox

FindAndSetColor.cs

// searches an arbitrary string
public static void FindStringAndSetColor(RichTextBox rtb, string key, Color color)
{
    int lastIndex = -1;
    do
    {
        int found = rtb.Find(key, lastIndex + 1, RichTextBoxFinds.None);
        if (found >= 0)
        {
            rtb.Select(found, key.Length);
            rtb.SelectionColor = color;
        }
        lastIndex = found;
    } while (lastIndex >= 0);
}

// searches the whole word
public static void FindTokenAndSetColor(RichTextBox rtb, string key, Color color)
{
    int newLineOffset = Environment.NewLine.Length - 1; // "\r\n" - "\n";

    int lineStart = 0;
    foreach (string line in rtb.Lines)
    {
        foreach (Match match in Regex.Matches(line, String.Format(@"\b{0}\b", key)))
        {
            rtb.Select(lineStart + match.Index, match.Length);
            rtb.SelectionColor = color;
        }

        lineStart += line.Length + newLineOffset;
    }

}