Pane can follow the operating system or stay on a fixed palette. System remembers one light palette and one dark palette and selects between them as the OS appearance changes. Fixed uses a third, independent palette. Switching modes never replaces any remembered selection.
New installations default to System with Light (rounded) for the light slot and Dark (sharp) for the dark slot; the remembered Fixed palette is Light (rounded). Existing configurations that only contain theme migrate to Fixed so their current palette remains exact. The legacy palette also seeds the matching System slot, while the opposite slot keeps its default.
Palette slots are validated at load, renderer, IPC, and persistence boundaries. Only palettes whose canonical base class is light can occupy the light slot, and only palettes whose base is dark can occupy the dark slot. Invalid stored fields are repaired independently and reported by the main process.
At startup the persisted config selects Electron's nativeTheme source. Main passes the four-field appearance snapshot through an argv argument and selects a cached, theme-specific BrowserWindow background colour. The preload decodes the snapshot synchronously; the HTML bootstrap resolves System against prefers-color-scheme and stamps the full class chain before React mounts. The provider then owns live OS updates, persistence, rollback, window controls, terminal, and editor updates. A versioned local cache and legacy localStorage.theme are fallback-only.
On Linux, System depends on the desktop environment and Chromium exposing prefers-color-scheme. Desktops that do not publish an appearance preference may remain on their reported default slot.