From the screenshot below, the menubar is translucent. The menu itself, although not well noticeable from screenshot below, is less translucent (and blurs out the objects behind).
Apple tells you why.
Apple wrote:The translucent Leopard menu bar appears on most computers that are equipped with a graphics card which is compatible with Core Image.
Some graphics cards, such as an NVIDIA GeForce FX 5200, may not have the necessary OpenGL capabilities to display a translucent menu bar even though they are compatible with Core Image. Those cards should render most effects, but not the translucent menu bar.
I am sure some users prefer solid colour through out the menubar. This is not a user-adjustable option directly from Leopard's System Preference. (Third party applications may be able to tweak this setting.)
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