Hi TAK,
Icons are just little images, set up in any application that can handle pixels. Cinema 4D as a might image machine can do that easily. There is no specific icon maker, well there is an artist doing it manually in C4D for MAXON.
Rick shows here a process to set one up.
http://www.cineversity.com/vidplaylist/python_scripting1/distributing_python_scripts
The way Cinema 4D stores those Icons, is inside the Application folder, and is typically the largest image in this folder, speaking of the default installation.
Just to be clear, I do not recommend to change this. However, the name in my current folder is “interface_icons_2x.tif” I guess the two times in the name is based to provide for my 5K screen the right quality. C4D picks based on the location the icon needed. I haven’t counted, but it certainly a four digit number (2000+).
You might get frustrated after a while, as each update might have a chance that this image will be updated as well. Which means your icons will be gone.
The most usable way I can think of, to change here anything, is to set them to monochrome, if one is working a lot in 3D stereo, with anaglyph glasses.
Fingers crossed, you have no trouble
All the best
