I also came to ask for the same feature.
I have a custom coloring that works WAY better than the default one, it shopuld be kept globally intead of just for each project.
I am doing a lot of small projects and I find myself having to open a completed project to copy paste the colors and transparencies everytime I start a new project (which is very often). It is a pain in the ass and it doesn't make much sense.
See attached captures of custom vs default layer color:
**DEFAULT**

**CUSTOM**
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