SetDepth lets you change your monitors depth (colors), but without having to launch the "Monitors" control panel. This is useful for artists, viewing pict/jpeg files, and programmers who need to switch between various color modes without having to launch the Monitors control panel every time.
You can switch your monitors depth from 1 bit (Black & white) to 32 bit (Millions of colors) all with the ease and convenience of command keys.
SetDepth utilizes a "Tail Patch" on "_MenuKey". It does contain a 'sysz' resource that asks for 5k in the system heap (under system 6.x).
SetDepth is written in both “C” and 68000 assembly language.
Why does it write to the System File?
SetDepth will behave as the "Monitors" control panel does, i.e., it will "*set the default depth" for the next reboot/restart of your Macintosh (in System 7.x only). (*Write (1 byte) to the system file)
Acknowledgements (for source code):
SetDepth uses “ShowINIT.c” source code to show the SetDepth icon at startup.
(Originally from: Paul Mercer, Darin Adler, and Paul Snively from an idea by Steve Capps)
Scott Knaster's book, “How to write Macintosh software”.