using System;
using System.Configuration;
using System.Drawing;

public class MyUserSettings : ApplicationSettingsBase
{
    [UserScopedSetting()]
    [DefaultSettingValue("white")]
    public Color BackgroundColor
    {
        get
        {
            return ((Color)this["BackgroundColor"]);
        }
        set
        {
            this["BackgroundColor"] = (Color)value;
        }
    }
}

string objectname;
if (TT.Properties.Settings.Default.Properties[objectname] == null)
            {
                SettingsProperty addprop = new SettingsProperty(objectname);
                addprop.IsReadOnly = false;
                addprop.SerializeAs = SettingsSerializeAs.Xml;
                addprop.PropertyType = typeof(string);
                addprop.Provider = TT.Properties.Settings.Default.Providers["UserSetings"];
                addprop.Attributes.Add(typeof(System.Configuration.UserScopedSettingAttribute), new System.Configuration.UserScopedSettingAttribute());
                addprop.Attributes.Add(typeof(System.Diagnostics.DebuggerNonUserCodeAttribute), new System.Diagnostics.DebuggerNonUserCodeAttribute());
                addprop.Attributes.Add(typeof(System.Configuration.DefaultSettingValueAttribute), new System.Configuration.DefaultSettingValueAttribute("0, 0"));
                TT.Properties.Settings.Default.Properties.Add(addprop);
                TT.Properties.Settings.Default.Save();
            }