using System;
using System.Drawing;
using System.Windows.Forms;

class Test : Form
{
  Test()
  {
    TextBox TextBox1   = new TextBox();
    TextBox1.Parent    = this;
    TextBox1.Text      = "Click Me";
    TextBox1.Click    += delegate
    {
      Color c = TextBox1.BackColor;
      TextBox1.Text      = "ReadOnly";
      TextBox1.ReadOnly  = true;
      TextBox1.BackColor = c;
    };
  }

  static void Main()
  {
    Application.Run(new Test());
  }
}

------解决方案--------------------

this.TestBox1.ReadOnly=true;
this.TestBox1.BackColor=Color.white;

------解决方案--------------------
//请再问下,在Enable=False的情况下,没办法改不改变字体颜色,我不想字体变成灰色

如果是这样的话,你试试使用TextBox1.ForeColor
1,readonly
2,backcolor | forecolor
如果不好使的话,再试试richTextBox吧,

------解决方案--------------------
C# code
            textBox1.ReadOnly = true;
            textBox1.ForeColor = Color.Black;
            textBox1.BackColor = Color.White;