/// <summary>
/// 获取无效时文本颜色
/// </summary>
/// <param name="backColor">控件背景色</param>
/// <returns>无效颜色</returns>
public static Color GetGrayColor(Color backColor)
{
Color controlDark = SystemColors.ControlDark;
if (RenderEngine.IsDarker(backColor, SystemColors.Control))
{
controlDark = ControlPaint.Dark(backColor);
}
return(controlDark);
}