just a word for your graphics designer about this
should be awesome for the entire phone to have the black or white choose on settings, personally i prefear black because save my eyes, but someone else could prefear white, grey is for '90 not 2019
GNOME applictions can be themed using GTK+ themes
I believe the decision to stick as close as possible to GNOME standards to be the preferable one. This way, if you theme your GNOME, you theme your phone.
When you customize the appearance of your GNOME Desktop, you don’t actually customize GNOME. You apply a set of preference for all the software rendered using GTK+ library.
Most (all?) apps in GNOME are written in GTK+ 3. Purism adapts these apps with their libhandy, a library which offers a GTK+ 3 widget. When you change your GTK theme, Librem 5 apps will be impacted too