title: Setting a ReadOnly TextBox default BackColor
body: <p>I have a <code>TextBox</code> which is set to be <code>ReadOnly</code>.<br>
  At some point that <code>TextBox</code> is being available for editing, and it's <code>BackColor</code> changes (It is indicating if the value is valid).<br>
  If I want to set the <code>TexBox</code> back to <code>ReadOnly</code>, the <code>TextBox</code> doesn't get back the original <code>BackColor</code> that a <code>ReadOnly</code> <code>TextBox</code> gets.<br>
  What should I do in order to get the original color again?<br>
  I realize I can set the color manually to <code>SystemColors.Control</code>, but is this the "right way"?</p>
  
  <h2>Code Sample</h2>
  
  <p>This is a simple code for demonstration.
  If <code>SystemColors.Control</code> is the way to go, I will change it in the <code>ReadOnlyChanged</code> event...</p>
  
  <pre><code>private void button1_Click(object sender, EventArgs e)
  {
      //At this point this.textBox1 is ReadOnly
      this.textBox1.ReadOnly = false;
      this.textBox1.BackColor = Color.Orange;
  
  
      /*this.textBox1.BackColor = SystemColors.Control;*/ //Is this the right way?
      this.textBox1.ReadOnly = true; //Textbox remains orange...
  }
  </code></pre>