Graphite Dark in graphite
Its sidebar was solid royal blue — the largest block of colour on the Desk, in a theme meant to be quiet charcoal. It is now graphite and flat, with a deep blue active item that ties it to the blue buttons and links, and the login panel follows. Text reads at 15:1 on the sidebar and 9:1 on the active item. If you had retuned its sidebar yourself, your choice is kept.
Upgrade
bench update # or: cd apps/nexus_theme && git pull
bench --site your-site migrate
bench build --app nexus_theme
bench restart