Seeing can be seeing things as brighter or seeing things as different colours. If ideas from describing sounds are available, then perhaps choose to re-activate these via the box of hearing.
If not, then suggest directly that the box of seeing needs two axes – how bright, and what colour.
The best description of light that we have is that it arrives in small chunks called photons – our eyes are not quite sensitive enough to notice each one arrive(5-8 photons enable a human to
see a flash of light), but nocturnal insects and some animals can do much better, down at the single photon level.
So there are two independent quantities: the brightness and the colour. You can see something brightly lit or only dimly lit in many colours, or only in red; brightly lit or only dimly lit, or only in yellow; something brightly lit or only dimly lit, and green. And there may be other colours you cannot see, and perhaps some things which are too bright or too dim to see(humans are not all that special, and physics tries to be universal, so build that in from the start).
The (simple) character of the photon sets the colour: choose a simple spinning arrow to describe a simple thing. The number of rotations a second is the frequency, which we may see as a particular colour (if the number of rotation second-1 is within the range of human seeing). So to represent different colours just spin the arrows faster or slower. That's how you can start to think about photons fruitfully: to find out why spinning arrows are so fruitful, you need to think more about brightness.