I do not know how to explain to a 6 year old how we are able to
perceive colour. Does anyone know how this can be explained?
Well, depending on the depth you want to introduce her to, it
can be difficult to explain to adults - much less children. You
explained the basics well enough. Without going to the molecular
mechanisms, here's a useful diagram: Light will pass through the
eye and Retina until it hits the Cones and Rods. That produces a
reaction (which I'll address next) - which then causes signals
to either resume or cease (Rods are, ironically, shut off by
light - not turned on). These signals pass through Ganglion
cells, through the Optic Nerve, and interpreted by the brain.
When some cells are switched on, like a 3-Way traffic stop, they
will prevent the information from other cells being transmitted.
A simple way of explaining it might be that inside our eyes are
millions of teeny-tiny molecules that act like light-switches,
and the brightness and color of light determine which of the
"light-switche