How do I know what you see?

It has,
on occasion,
come to my
attention
that I and you
see different
colours
of a thing.

I know a child,
of great intellect
and acumen,
his insights
are appealing,
yet he insists
that green is blue,
and further,
that blue is green.

We have agreed
that this is
less a breech
of reality,
and more
a proof
that reality
is unconcerned
with our
agreements.

We, he and I,
consider this matter
at rest.