To celebrate its diversity
South Africa became the rainbow nation.
There are a few problems with this.
Black isn’t on the rainbow.
White isn’t on the rainbow.
Brown isn’t on the rainbow,
pink isn’t on the rainbow
no-one’s actual skin colour is on the rainbow.
How is this when rainbows show every type of light?
Our eyes have only three colour-sensors
so can’t tell a mix of blue light and green
from the aquamarine that lies in between
but know red plus purple isn’t myrtle
so you invent a colour, magenta,
discover the rainbow is not enough
you must have pink.
This prompts us to think that
things reflect the whole spectrum
to different extents.
But some colours don’t exist if they get too intense
To find brown, tone things down
cause the same light
can look orange or yellow
like gray looks white
if the dimness around it makes it look bright.
The amount reflected matters too.
Look, what I’m trying to say to you is colour’s complex,
context dependent, curiously hard to see
how we can judge by the colour of skin
whatever kind of content lies within
when we can’t even pick out from that shade
the actual light waves overlaid so
when we talk of a rainbow of people or preferences
understand that our language has limited references
because people don’t fall onto lines
any more than they fit into boxes,
a spectrum is too small an infinity to capture personality
so if you’ve dared to have a dream
where real people can be seen
because they know what eyes and words don’t show
then you can find me
somewhere over the rainbow
 There are 4 types of light-sensing cells in eyes, but the three cone cells (2 in the colourblind) are the ones that mainly judge colour. The other cells, rods, specialise in low-light or peripheral vision, and don’t compare results to other cells in order to judge shade most of the time, although they may help in low light. There are, however, a small number of humans with 4 distinctly different cones – functional tetrachromats, who may have higher levels of colour vision.
 This is effectively wrapping together the ends of the spectrum to make a loop.
 Dark red can also appear brown.
 Large amounts of colour vision are ‘filled in’ by the brain, due to the concentration of red and green cones in the fovea – outside the middle of our vision, colour perception is very weak for non-blue colours.
 This refers to a slightly technical point about the mathematics of infinity. It can be shown that there are several different types of infinity of differing size. All of the following depend on what assumptions are made about how numbers work, but the most common version is: we can say that the ‘smallest infinity’ is the number of whole numbers (1,2,3…). This is the same as the number of even numbers, as doubling each whole number gets an even number: there is a one-to-one match, so there must be the same number of numbers (even though there are clearly whole numbers that aren’t even). However there are definitely more numbers of any kind between, say, 0 and 1, than there are whole numbers. This is proven by Cantor’s diagonalisation argument. This is usually identified as the ‘next highest infinity’, the continuum, which is the infinity of a (non-pixellated) rainbow. Eyes can only distinguish between a few million (brightness-limited) colours, so can’t even manage the lowest infinity. However an object’s reflection is a function of the light wavelength being reflected with a different possible value at every point in the spectrum. The list of all possible reflection functions is a ‘power set’ of the rainbow, and power sets of infinite lists are always a higher infinity than that of the list. There are a few mathematical caveats that mean this may or may not be true in practice.