The Colours of People

Everywhere you look, there are people. Different sizes, different shapes, different colours. And that’s pretty awesome.

But why do I have green eyes, my mum has blue and my dad has hazel?
Why is my hair a shade of browny blonde but my sisters is almost black?
And why oh why do I have to roast myself in the sun to get any form of tan that some people just have naturally??

 

greeneyes


All of the colour differences between people stems from pigments – any substance found within our cells which colours us in some sort of way.

It is the special kind of pigment, melanin which is to blame for any of your 3 major body colourings: eyes, hair & skin. 

Melanin

Melanin is made within melanosomes which are found in cells called melanocytes.

Three important types of melanin include:

  1. Eumelanin = dark pigment 
  2. Phaeomelanin = light pigment 
  3. Neuromelanin = responsible for colouring regions of the brain – problems with neuromelanins are linked to Alzheimers and Parkinsons diseases.

The amount of these types of melanin we each get is determined genetically.

 

Melanindiagram

Eyes

In our eyes, the melanin is found in the iris (the coloured part surrounding the pupil). The top layer of the iris is called the stroma and this is where those melanocytes are found.

Eyediagram

More melanin will result in dark brown or black eyes. With over 55% of the world rocking them, brown eyes are the most popular eye colour.
Less melanin means blue, green or hazel eyes. Green eyes are the rarest in the world with approximately only 2% of the worlds population having them. 

Skin

In our skin, those melanocytes are commonly found in our deepest layer of skin, the basal layer. There are many factors which determine skin colour and it comes down to the size, distribution, shape and number of melanosomes plus how active the melanin within them is. It also takes into account the gene protein melanocortin 1 receptor (MC1R).

redheadMore MC1R activity = more eumelanin, less phaeomelanin. 

Some people have sort-of faulty MC1R genes and they are likely to have red hair, pale skin and freckles. 

Very simply, if you have high amounts of eumelanin but low amounts of phaeomelanin, the resulting skin will be black or brown. If you have low amounts of eumelanin but high amounts of phaeomelanin, the resulting skin will be light (freckles are likely too). People with very little levels (or none at all) of both eumelanin & phaeomelanin will have extremely light skin, this is known as albinism.

What about tanning? The more you expose skin to ultra-violet (UV) rays from the sun, the more melanin the skin produces. This will result in darkening the skin and helps to protect skin from any more damage. sun
Back in the day when most people huddled around the equator, they got a whole lot of sunlight and therefore a whole lot of vitamin D too (from the UV radiation).
We need vitamin D to help prevent illness such as rickets or soft bones so when people started moving away from the sun and dispersing to different, darker parts of the world, their bodies began to compensate for this loss of sunlight and the resulting loss of vitamin D. This happened by lower levels of melanin being produced and the lightening of skin, so more sunlight would be able to be absorbed. 

Hair

When it comes to hair, I barely know whether to describe mine as brown, blonde, muddy blonde, light brown? Sometimes I see strands of red and sometimes strands of black? It’s a bit of an identity crisis situation. 

You see, just like out skin, hair contains eumelanin (dark pigment) and phaeomelanin (light pigment). The density and the dispersal of the different types of melanin and their pigments will also contribute to differing hair colours, which can also happen across the space of one head. 

There is brown eumelanin and black eumelanin. 
If only a small amount of brown eumelanin is present, the resulting hair colour is blonde. Larger amounts of eumelanin will produce brown, dark brown and black hair. 
For red-heads, phaeomelanin is the dominant pigment which people with dark hair also sometimes produce. However, the darkness of their hair, thanks to eumelanin, overpowers the light pigment. In my case where I see hair strands that are red, light brown, and blonde, it is likely due to some phaeomelanin being produced. Grey hair is when only a small amount of melanin remains in the hair while white hair is the complete absence of melanin.

hair

There are so many variables in our hair, skin and eye colours and that makes a pretty cool world full of unique and interesting humans. We’ve heard it before, but really, if we all looked the same, the world would be a pretty boring place! 

Do you see what I see?

Hello, hello. Welcome back to my wonderful world of colour.

Or in this case, perhaps not?

I just took this test here.

Luckily for me, I am part of the 94.5% of New Zealand‘s population that doesn’t exhibit signs of colour blindness.
I am one of the lucky 259 women who can identify a blue hue from a purple one, the 260th woman might see them both as blue. For men, colour blindness is much more common with 1 in 12. 

And when I say luck, for the majority of cases, being colour blind is almost a luck of the draw.

You see, colour blindness is a genetic mutation passed down from your parents.
The affected gene is carried on the X chromosome.
Women carry two X chromosomes (XX).
Men carry one X and one Y chromosome (XY).

You get one sex chromosome from your mum (it’s going to be an X, that’s all she has).
You get your second sex chromosome from your dad (it could be X, making you a girl orrrr it could be Y, making you a boy). 

The genetic family tree below shows the potential offspring of a non colour blind female who carries the mutated gene on one of her X chromosomes AND a non colour blind male.

genepool.png

Both X chromosomes must carry the affected gene for a girl to be colour blind meaning her father MUST be colour blind.  Only having one affected X chromosome will result in that girl being a carrier and she may or may not pass on that X affected X chromosome to her own children. 

Colour blind men can only pass on affected X chromosomes to their daughters, as boys get their Y chromosome from their father. 

Naturally speaking, nobody can determine whether you will be a boy or a girl.
Nobody can determine whether you get your mum’s dud X gene carrying the colour-blindness genetic mutation or you get her other one.
So the way I see it, it all comes down to luck.

As I mentioned in my last blog, two clever guys by the names of Thomas Young and Hermann von Helmholtz came up with the trichromatic theory of vision involving colour receptors. You can read all about it here. 

cones

Our red, green & blue cone photoreceptors! 

At the back of the human eye, there are cone photoreceptors and rod photoreceptors. For the majority of cases, it is faults within the cone photoreceptor cells which lead to differences in the way a person might see colours.

Colours through normal vision (when all three cones are in good working order) generally look a little something like this….

colourblindew
However, have a browse through my table and have a look at how the different kinds of colour blindness affect the way in which these colours are seen. 

table

For people who are colour blind, some tasks in life can be made pretty tricky. This includes, but is not limited to, interpreting traffic light signals or coloured charts, or as simple a task as picking ripe fruit and veges at the supermarket. 

Unfortunately, there is no cure. However, it’s not all bad news. Modern technology advancements have contributed to helping out our colour blind pals. Apps have been created to help coordinate colours specifically for those trying to find an outfit that doesn’t clash. Some apps allow for a photo to be taken and all of the colours within that photo are then able to be identified with a simple tap of the finger. 

Also, technology in the optical world has now made colour-correcting glasses for people with red-green colour blindness that look exactly like any other pair of glasses. Which is pretty damn cool.

So next time you’re picking out those bananas at the supermarket and you can easily tell which ones are ripe and which are not, be grateful that you aren’t in that small, unlucky 5.5% of New Zealand’s population.