BackColor does not work

BackColor can not work. Is it obsolete? I can not find them from intellisense of VS, too. There is no any indication for this. But it really broke my code. :(

Code example:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using ActiproSoftware.SyntaxEditor;
namespace TestforActipro
{
public partial class Form1 : Form
{
SyntaxEditor m_editor = new SyntaxEditor();
Button m_button = new Button();
public Form1()
{
InitializeComponent();
Controls.Add(m_button);
Controls.Add(m_editor);
m_button.Click += new EventHandler(button_Click);
}

void button_Click(object sender, EventArgs e)
{
m_editor.BackColor = Color.FromArgb(125, 125, 125);
m_editor.Refresh();
}
}
}