how to give the color of changable word character

Question

i am trying to give yellow color on changeable character

 

diff.aspx  

 

 <asp:TextBox ID="firsttextbox" runat="server" TextMode="MultiLine" Width="500px" Height="200px"></asp:TextBox>

<asp:TextBox ID="secondtextbox" runat="server" TextMode="MultiLine" Width="500px" Height="200px"></asp:TextBox>

<asp:Button ID="Button1" runat="server" Text="Compare" OnClick="btnCompare_Click" />

 <asp:Label ID="lblfirst" runat="server" Text=""></asp:Label><br />
            <br />
 <asp:Label ID="lblsecond" runat="server" Text=""></asp:Label><br />

 

 diff.aspx.cs

 

protected void btnCompare_Click(object sender, EventArgs e)
{
    //some code
    lblfirst.Text = "param1:" + string.Join(" ", getWordthatUpdated);
    lblsecond.Text = "param2:" + string.Join(" ", getUpdatedWordOfSlist);
}

    

 

I am trying to give yellow color on s character only 

 

need help