The number of the ELAC or SEC below the control surface; the hydraulic jack colour and the arrow shows the chain of control.
So for example: normally the left aileron is controlled by ELAC 1 using only the Blue Hyd jack. If ELAC 1 or Blue Hyd fails, control passes to ELAC 2 using only the Green Hyd jack.
The left elevator is normally controlled by ELAC 2 using the Green Hyd jack. If ELAC 2 or Green Hyd fails, control passes to ELAC 1 using the Blue Hyd jack. Or, if ELAC 1 and 2 have failed, control passes to SEC 2 using the Green Hyd jack, etc.
On each surface, the jack not in use performs a damping function - its hydraulic fluid is put into a closed loop which damps the control surface; preventing flutter etc.
