The colours of the indicators are not the main problem when safety is in question.
The only thing that matters is whether the robot is safe or not.
If the power link is IN then the robot is potentially unsafe.
If it is out and the weapons disabled and locked, then it is safe.
A lit LED or other indicator proves only one thing, that the LED works and it has power to it.
It says nothing about the device controlling the LED or its logic state.

We have all seen the car, with its right indicator flashing, turning left.

The same applies to robots, what do you do when the link is in and the lights are off? or the lights are on and the link not in?, both indicate that the robot is unsafe, i.e. in just the same state as a robot with its power link in and without any indicators fitted.

Robot systems are notoriously unreliable at the best of times, even before they are damaged in battle.
Home made or home installed systems to indicate the state of the power or failsafes are just as liable to failure as the robot they are in.

I run a robot event each year here in Somerset and work to the following safety guidelines:-

1. The robot gets a technical inspection to prove it and its failsafes operate correctly when it arrives at my event.
2. It is only powered up and its weapons locks removed when it is in the arena.
3. The arena is strong enough to contain it whatever it may do. If the robot is potentially too powerful for my arena, (such as Hypnodisc), then it does not get powered up.
4.The link is taken out and its weapons made safe before it comes out of the arena.
5. All tests after repairs are done in the arena and are supervised by me or my appointed deputy.
6.At no time is a robot powered up in the pits area.
7.If a robot in the arena does not respond to its controller then it is treated with extreme caution until made safe by some one competent.

If you stick to these rules then you do not need indicators of unknown reliability.

I have no problems getting full insurance cover for my events. The insurance company accepts the above rules and my certificated competence from previous work experience.

This is not meant as any criticism of the FRA rules, I am just pointing out that safety indicators may not be reliable and dont help to make an event safer.