Problem with color text in RichTextBox

[alex berd]

Hello dear experts

My problem is color of text in RichtTextBox

If I type the text in RTB and using this code:

public Boolean blueHighLight(String _word, int startCoordinate, int endCoordinate){
this.inputTextAreaRtb.SelectionStart = startCoordinate;
                this.inputTextAreaRtb.SelectionColor = Color.DarkBlue;
                this.inputTextAreaRtb.SelectionFont = new System.Drawing.Font(
                "David",
                12, FontStyle.Underline);
                this.inputTextAreaRtb.SelectedText = _word;
}

It works perfect!

But if i try to import text from file using:

String[] splitFindings = Regex.Split(_findigs, @"(?<=[ ])");
            foreach(String word in splitFindings)
            {
                this.inputTextAreaRtb.Text += word;
                String wordWithoutPunctuation=Regex.Replace(word,@"(\p{P})","").Trim();
                if (this.blueHighLight(wordWithoutPunctuation, this.inputTextAreaRtb.Text.Length - word.Length, this.inputTextAreaRtb.Text.Length))
                {
                    .....
                }

I have no result

Have any ideas why?

[EARNEST]

please use CODE tags

[alex berd]

Sorry i`ve change the question

[alex berd]

Sorry i`ve change the question