Descriptions of the human race based on racial characteristics go back to the late seventeenth century.
In 1684, a French doctor, François Bernier, published Nouvelle division de la terre par les différentes espèces ou races qui l'habitant" which proposed four different face and body types: Europeans, Far Easterners, Lapps and Blacks.
In the eighteenth century, Carl Linnaeus made specific reference to skin colour in his system of categorization: Europeanus (white), Asiaticus (yellow), Americanus (red) and Africanus (black).
Linnaeus' pupil Johann Blumenbach, sometimes described as the founder of modern anthropology, added a fifth grouping, Malay (brown).
The idea of categorizing people according to their colour - "colour taxonomy" - greatly interests Trevor Phillips.
A prominent member of the Afro-Caribbean community, Trevor wants to know how and why this system took hold.
He wants to know why a system based on skin colour should have had such a profound impact on relations between races.
He wants to understand what role these categories might have had in shaping modern day racial prejudice, belief and behaviour.
Trevor asks: "What is it about colour that matters so much? We know what lies beneath the skin - melanin.
But this isn't just a chemical thing.
This is about something deeper and more atavistic.
It caught on because it corresponds to some human need or maybe some human memory.
But it's hard to say why, especially when most people's colour isn't actually what the word says.
White people are really pink or cream, black people are brown, red people are bronze etc.
And within every group, there's a massive range of colour."
At the same time, Trevor recognises that a combination of political liberalism and mobility is transforming our racial concepts.
Trevor wonders whether a taxonomy based on differentiation by colour is still sustainable.
He says: "For a whole series of reasons there is a fundamental sea change going on in our heads that might spell the death of the Linnaean classification.
We are mixing more than ever before.
Britain is a leader - mixed race is the largest, youngest and fastest growing group.
Many of our brightest stars are mixed race.
With more and more people living and loving all over the globe, surely this is the future.
No simple system of racial categorisation could survive this kind of mixing."
If colour ceases to be a meaningful description, what happens to racial identity? Does it wither away? At what point does racial mixing signal the transformation of both communities into something new?
Trevor doesn't have answers to these questions.
But he's very keen to investigate them.
Producer: John Watkins.
Trevor Phillips asks why we define members of the human race by the colour of their skin."