Suppose you’re working on multiple forms and you’ve got a visual dependency on data in one or more forms (something like the Aero effect in Vista). In such cases, use the form’s Opacity property.
First, set the foreground form’s Opacity to less than 1. This technique is also useful when the background form is being updated by a child thread, and you’re simultaneously working on the foreground form?which depends on the data in the background form.
//Set the Transparency to 50% frmMain.Opacity = 0.5;