用picturebox写的一个按钮控件，为什么鼠标离开的时候，有时候是变回 SystemColors .ButtonFace ;颜色（正常），有时候却鼠标离开后还是Color.White 呢？ 费解！请高手指点迷津！谢谢
 public partial class ImageButton : System .Windows .Forms .PictureBox 
    {

        private Color _mouseOnBackColor =Color.White ;
        private Color _BackColor =  SystemColors .ButtonFace ;
        private Color _mouseDownBackColor = Color.SkyBlue ;

        public ImageButton()
        {
            InitializeComponent();
            this.MouseEnter += new EventHandler(ImageButton_MouseEnter);
            this.MouseDown += new MouseEventHandler(ImageButton_MouseDown);
            this.MouseUp += new MouseEventHandler(ImageButton_MouseUp);
            this.MouseLeave += new EventHandler(ImageButton_MouseLeave);
            this.Size = new Size(25, 25);
            
        }

        void ImageButton_MouseLeave(object sender, EventArgs e)
        {
            this.BackColor = backColorMouseOut;
            this.BorderStyle = BorderStyle.None;
        }

        void ImageButton_MouseUp(object sender, MouseEventArgs e)
        {
            this.BackColor = backColorMouseOn;
            this.BorderStyle = BorderStyle.FixedSingle;
        }

        void ImageButton_MouseDown(object sender, MouseEventArgs e)
        {
            this.BackColor = backColorMouseDown;
            this.BorderStyle = BorderStyle.FixedSingle;
        }

        void ImageButton_MouseEnter(object sender, EventArgs e)
        {
            this.BackColor = backColorMouseOn;
            this.BorderStyle = BorderStyle.FixedSingle;
        }

        [Description("按钮背景颜色"), Category("Appearance")]
        public Color backColorMouseOut
        {
            get { return _BackColor; }
            set { _BackColor = value; }
        }

        [Description("鼠标在按钮上面时的背景颜色"), Category("Appearance")]
        public Color backColorMouseOn
        {
            get { return _mouseOnBackColor; }
            set { _mouseOnBackColor = value; }
        }

        [Description("鼠标在按钮上按下时的背景颜色"), Category("Appearance")]
        public Color backColorMouseDown
        {
            get { return _mouseDownBackColor; }
            set { _mouseDownBackColor = value; }
        }


    }