TL;DR I'm attempting to locate the system files/variables responsible for drawing the menu bar in Sierra so that I can tweak the color and opacity, and would love any information you might have on the subject.
In the past, the resource files that held the bar's configuration exited in SArtfile.bin files. These have been done away with in favor of Resource.car files, the relevant ones housed in /System/Library/CoreServices/SystemAppearance.bundle/Contents/Resources.
I've messed with these via ThemeEngine to remove the stoplights in title bars and change various other system icons and colors. It seems that the only thing that these files do for the menu bar is provide it it's logo, which I've been able to change successfully:
Unfortunately, the logo is the only menu bar resource provided by these .car files, unlike their older counterpart the SArtfiles. This means Apple changed the way they draw the menu bar in a way that makes it harder to modify. Along with searching the .car files, I've checked various plists and the defaults command and have found nothing at all relating to the menu bar.
I am aware of programs like Flavours 2 which tweak the menu bar by overlaying graphics, but that's a terrible hack that breaks pretty often. I want to change the color of the menu bar itself rather than pretending that a different program is the menu bar. As far as I know, this hasn't been done before in anything including and past Yosemite.
Does apple or any book document the code that performs this function?