When the device is rebooted (after running out of battery, or a ‘magnet’ reboot), it alternates between 2 states : update mode (FOTA) and application mode.
In update mode, the LED is solid BLUE after reboot (takes about 5s to reach). In this mode, the device waits for a connection from the ‘upload’ devtool to load a new firmware version. If after 60s it has had no connection, it changes to a solid WHITE LED for 5s and then automatically reboots (and will therefore go into application mode). Whenever you want to update the firmware version of the device, you should first force it to reset and enter the update mode.
In application mode, the LED will initially be shades of RED while it boots up the main application. During this time, the screen will (after about 30s) show a splash screen with the current firmware versions.
Finally, the LED will go yellow while it connects to a network (flashing green or red depending on the result), and then enter the main application screen : either the logo+QR code if unallocated, or the home dataview screen if allocated.