At work, all black, because I prefer working in a darkened room and sometimes I need to use the laptop in sunny conditions full of glare. I have no need of any extra light getting blasted at me not directly related to something I'm working on. Also, I get a kick out of the "Why are your other monitors off?" comments. Also, IT tends to clutter my desktop with a bunch of shortcuts with a hodgepodge of icon styles, it's a lot easier to visually parse these on a black field.
At home, the media server is directly connected to a TV with HDMI and has a desktop environment. My distributions default wallpapers always come in two varieties, colorful or greyscale. The server automatically logs into a restricted user account for family access to Kodi, retro arch, web browsing, etc., which has the colorful wallpaper. If for some reason I need to get into the admin account with a GUI, the desktop wallpaper is grey. It's like an always-on simplified color coded whoami. Since I almost never interact with this machine except through ssh or the services it hosts, this is the most amount of ricing I'm willing to do.
Is that a statue of the god of F1?