The counter staff cannot let you through.
You have to go up higher amd appeal.
Call or visit the TP and explain to them, and ask them how they can
help.
The TP are very nice people (at least the ones at Comfort Driving
Centre are).
I think they will allow special cases if they deemed it to be
safe.
Expect them to test you further or require you to furnish a medical
report.
Knowing the positions of lights is helpful, but there are some
lights that will cause you difficulty. Like The arrow, some
junctions have a single arrow light that flash red, green and amber
accordingly. You must be able to distinguish them. Some carparks
and crossings only have one light for green and red, some have two,
placed horizontally. These easily can cause confusion, especially
if you are in an unfamiliar place.
The criteria for allowing you, is whether you can sufficiently
identify the various signal lights.
Its for your own safety and others.