Hi, I read that the way to change the color of the header bar in split screen mode is to go to mac’s system settings and change the accent color, which works… for every color except graphite, the one I want. When I change the accent color to graphite, the currently-used window’s header bar inexplicably becomes purple. Might anyone know why that is/how to fix?
This thread might help: About the color of the header
I eventually got used to it, but now you’ve reminded me, I’ll not be able to unsee it for weeks 
Aside: Lock in Place is even more bizarre. I find that so confusing, I had to stop using it.