Hello! I've been customizing my OS X installs since 10.5 with various programs (ThemePark, (S)artFiletool, and most recently Alex Zielenski's ThemeEngine[0]). I'm a fan of the `platinum' theme from Mac OS 9, so I've been creating a system-wide OS-9 theme in my spare time this past ~year. I have .car files available for Yosemite and El-Capitain (the version I'm currently using). The Yosemite files are (mostly) true to the old OS 9 aesthetic, but I thought I'd change up the look of the traffic lights on el-capitain and release it at some point [1]. I have the source files for each different design I've done, along with the Assets.car (the replacement for the deprecated [and absent in 10.11] SArtFile.bin), SystemAppearance.car (change highlight colors in menubar and right-click menus/make window masks sharp instead of rounded [yes it also affects the GraphiteAppearance.car window masks]), and the GraphiteAppearance.car (used for the platinum traffic lights) files. At some point I will finish both of these and release them, but for now (I just finished my summer job working for one of my professors/I'm on vacation at the moment) the Yosemite theme remains slightly incomplete, and I've got some more testing to do on El-Capitain. Also gotta port that Yosemite-System-fontpatcher project to work with the new San Francisco (let's not get that confused with susan kare's 1984 `SanFrancisco'! [2]) typeface so I can finally get Charcoal/Chicago as my system font again like it was in Yosemite...
[0]: https://github.com/alexzielenski/ThemeEngine
[1]: http://i.imgur.com/fpZemvX.gifv
[2]: http://i.imgur.com/Q1tZknV.png