What does a blue A/THR FMA in column 5 of the FMA indicate?

A blue A/THR in the Flight Mode Annunciator (FMA) indicates that the autothrust system is armed but not actively engaged. In the context of the A320's autothrust system, being "armed" means that the autothrust will take control when the aircraft is in a suitable flight condition, such as during the takeoff or climb phase.

When the autothrust is armed, the system is ready to automatically adjust thrust as required based on the aircraft's speed and altitude, providing a layer of automation and efficiency in power management. This helps the pilots maintain optimal performance without having to manually manage thrust.

The other options are not applicable in this context. If autothrust were engaged, it would display differently, reflecting active thrust management. Similarly, if autothrust were off, the FMA would indicate that the system is completely inactive. Lastly, being in the N1 mode refers specifically to a different operational state of the autothrust, which would not be indicated simply by the blue armed status.