I had forgotten I’d even found and tried this until I looked up at my menu bar today after changing my desktop image and noticed it was opaque. I can’t find the site where I originally got the code, but I’ve found another blog that mentions it. The code to execute at the command line is:

sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 0.63

(The code all needs to be entered on one line, of course; I need to work on my CSS for displaying code, probably employing Google’s Syntax Highlighter. So add that to my gigantic and ever-growing — at an increasing rate — to-do list. At my present trajectory, I will get this done approximately 10 million years after never.)

As the poster notes, the number 0.63 at the end can be any decimal value from 0 to 1. It represents the lightness of the opaque menu bar: 0 is black, 1 is white, and anything in between is shades of gray (surprise!); all non-white values have a subtle gradient as well.

This works great, which is not surprising, since this is the way Apple designed it to be managed. (In other words, they didn’t intend for the end user to be able to adjust it at all… but they built a way into the code to allow their programmers to adjust it.)

Of course, in the meantime since I first complained about it, I have actually come to tolerate (if not like) the translucent menu bar. But for now I’ll leave it as it is. If I do decide to change it back, I’ll run this:

sudo defaults delete /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables'

And of course, because these are system-level changes, you need to reboot for them to take effect (which is probably why I had forgotten I’d done it in the first place; I didn’t restart immediately and surely got distracted by whatever it is in my life that’s constantly distracting me… two kids, perhaps).