Form Transparency
In addition to the properties that specify how the non-client area of a form are rendered by Windows, the Form class provides a set of properties that allow you to change the appearance of the form as a whole, including making it partially transparent or removing pieces of the form altogether.
The property that governs transparency of the entire form is called Opacity and defaults to 1.0, or 100% opaque. A value between 0.0 and 1.0 denotes a degree of opacity using the alpha-blending[7] support in more modern versions of Windows, where any number less than 1.0 results in a form that is partially transparent. Opacity is mostly a parlor trick, but it's kind of fun for making top-level windows less annoying than they would normally ...
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