Without speculating on precisely what flavor of Suck they were drinking in Cupertino the day Apple decided to make the Leopard menu bar transparent, can we just stipulate that for some users, at least, the imposition of this unwanted "feature", without the courtesy of being granted any sort of choice, is so annoying that we'd be willing to pay $100 just for the satisfaction of reaching down the back of Steve Jobs' jeans and giving him the biggest wedgie of his reality-distorted life? It is with a sense of indomitable smugness, therefore, that we observe that the nut has been cracked, the Gordian knot cut, and the ravelled sleeve knitted up. Someone has found the magic setting that restores to the menu bar its rightful and peacefully solid opacity.
The place to look is Steve Miner's blog. There are two approaches listed here, one rather dangerous and tricky, the other much easier and simpler. The first involves editing a .plist file, which can be difficult, not least because serious permissions issues can arise that can render your Mac unusable. The second, which you'll see if you scroll down the comments a little, proposes that you do the very same thing by a simple command in the Terminal.
Here's what to do. Copy the following into TextEdit and rejigger it so that it appears all on a single line (that is, delete any Return characters):
sudo defaults write
'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 1
Now copy that line. Start up Terminal, wait until you see the prompt, and choose Edit > Paste. If what you copied didn't include a final Return character, you will now have to press Return. In any case you'll be asked for your password. Nothing visible will happen afterwards, so you must now restart the computer to see whether the menu bar has turned opaque. (Don't bother logging out and in; that isn't enough. You really must restart the computer to get the change to "take".)
Your menu bar will now be very, very opaque - and very, very white, and very, very flat-looking. To fix the whiteness and the flatness, you have two choices.
One possibility is to turn the menu bar grey, as in Tiger. To do so, enter the same command in the Terminal that you gave before, but put "0" instead of "1" at the end. Or, as one reader over at MacOSXHints has suggested, try a value of "0.63"; apparently this is the most Tiger-like setting of all. Remember, you'll need to restart the computer again afterwards. This is the solution I am currently using, and I really like the way it looks.
The other possibility is to place a dash of color tinting over the white menu bar. To do so, turn to the redoubtable Peter Maurer. In his blog, he reveals that he had in fact already written an application for conquering the menu bar's transparency, but when Leopard went final, it stopped working, so he withdrew it. When combined with Steve's .plist trick, though, it does work, so he has re-released it under the name Menu Bar Tint.
Download Menu Bar Tint, install it somewhere useful, and start it up. Menu Bar Tint must actually be running in order to operate, so immediately go to the Login Items in the Accounts preference pane and drag Menu Bar Tint into the list from wherever you installed it.
You now have Menu Bar Tint's preferences window showing on your screen. (If you don't, double-click Menu Bar Tint in the Finder.) You must now set three color preferences that will be used to generate a gradient of color over your menu bar. For each one, click the color rectangle to summon the Colors dialog. In the Colors dialog, pick a color, and (this is important) don't forget to set some opacity using the Opacity slider at the bottom of the dialog, because if you don't, your colors will be completely transparent and therefore you won't see anything happening. The painting of color over your menu bar is live, so you can experiment and view the results in real time. Menu Bar Tint also has some settings for making the overall transparency of your colors different when the mouse is over the menu bar, but I don't like that effect, so I set the two sliders in the Menu Bar Tint preference dialog to the same value.
Menu Bar Tint is very clever, but it doesn't know enough to shut itself off when some application (such as DVD Player) goes into full screen mode, so I prefer to run without it for now.
And what if we change our minds and want to undo our settings entirely? In the Terminal, the following will restore the dreaded menu bar transparency:
sudo defaults delete
Again, you want that all on one line, neatly arranged in TextEdit, before you enter it into the Terminal. And you want to be really, really, really careful, because if you get this wrong you will hose the WindowServer .plist file completely and your computer will be unable to start up (though I suppose the file must be backed up in Time Machine, so presumably you could fix things somehow, in a pinch, from the backup).
The really big question that remains unanswered at this time is: what else might be the consequences of the setting that we've changed here? Will Core Image behave differently in any other ways, apart from changing the manner in which the menu bar is drawn?