You are using the wrong phrase I think. If you mean the "Title Bar" then have a look at the solutions to this CP post:
Changing Color Title Bar[
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Alternatively, if you want to change the color of the MenuBar on your form then have a look at this post
How to change background color of menustrip in windows form?[
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If you meant something else entirely then I suggest you try to be clearer when phrasing your questions. You should also try to be accurate with your tags - you've tagged this as WPF but refer to Windows Forms in your question.