You can get the panel out of the Controls collection using LINQ and the name of the Panel that you want to work with. This gets a panel out of the collection that has the name "panel1".
var p = from c in this.Controls.Cast<Control>()
where c.Name == "panel1"
select c;
Panel pan = (Panel)p.FirstOrDefault();
From there you can do whatever you want with it, make it visible, invisible, change the background color.