Get selection text of RichTextBox silverlight 5

Hello,

I can not continue get selecting text after apply color for selection text.

richTextBox1.Selection.ApplyPropertyValue(TextElement.ForegroundProperty, new SolidColorBrush(Colors.Blue));
                                richTextBox1.Selection.ApplyPropertyValue(TextElement.FontWeightProperty, FontWeights.Bold);

This is my code:

//Content of richTextBox1: "Change color for selecting text"


// Get text1 = "color"
int startIndex = 7;
int Length = 5;
TextPointer start1 = richTextBox1.ContentStart.GetPositionAtOffset(startIndex + 2, LogicalDirection.Forward);
TextPointer end1 = richTextBox1.ContentStart.GetPositionAtOffset(startIndex + 2 + Length, LogicalDirection.Forward);
richTextBox1.Selection.Select(start1, end1);
string text1 = richTextBox1.Selection.Text;
//text1="color" ( it is right :) )
// Apply color for text1
richTextBox1.Selection.ApplyPropertyValue(TextElement.ForegroundProperty, new SolidColorBrush(Colors.Blue));
richTextBox1.Selection.ApplyPropertyValue(TextElement.FontWeightProperty, FontWeights.Bold);

//Continue: get text2="selecting"
startIndex = 17;
Length = 9;
TextPointer start2= richTextBox1.ContentStart.GetPositionAtOffset(startIndex + 2, LogicalDirection.Forward);
TextPointer end2 = richTextBox1.ContentStart.GetPositionAtOffset(startIndex + 2 + Length, LogicalDirection.Forward);
richTextBox1.Selection.Select(start2, end2);
string text2 = richTextBox1.Selection.Text;
//text2 is "for selec"   (It it not right :(, I want to get "selecting" :(()

Can you help me?

Thank you.