There are two fuel transfer valves between each outer tank and its associated inner tank.
Both transfer valves should open when its associated inner tank gets down to approx 750 kg, and all the transfer valves should shut again at the next refuelling. If one of a pair fails, the other should still operate.
The amber indication occurs when either of a pair of valves on that side is open or partially open. If one valve opens or partially opens in flight, the worst that can happen is that your outer tank fuel drains into the inner tank too early, (which you will be able to see by looking at the contents of each tank on the fuel page), So you can still use all your fuel - the only issue is a loss of wing bending relief.
If both transfer valves on one side fail shut - very unlikely but theoretically not impossible - then you might have 700kg less fuel available at the end of your flight.
In these stupid times of carrying minimum fuel, one would asses the weather, number of runways and traffic flow etc., and if necessary might opt to use some of your diversion fuel to commit to the original destination. If weather or traffic was against you, the loss of 700kg could prompt a pan or mayday call, I would suggest.