I have blonde/brunette/red hair, and I'm proudly an Asian.

Don't you just have a thought that they're looking gorgeous in those hairs?
Don't you have a second wishing you have blonde hair? brunette? or maybe vivid red?
Yes? Brunette hair colour, blonde hair colour, red colour hair aren't privilege for american nor english anymore.
We often see people with various hair colours. Some are natural and some are dyed.
Hair colour dyeing used to be only for elderly person. But this is no longer the fact, hair colouring is very popular nowadays, there are a lot young adults dyed their hair due to the influence of celebrities with different hair colours such as red, blonde, brunette and others.

People used to dye their hairs by using natural colourants from plants and minerals. These natural colourants they used contain pigments and natural bleaching agents, which can cause reactions that change the hair colour. Some popular natural colourants are henna, walnut shells and vinegar.
The natural pigments of these colourants generally work by coating the hair shaft with colour.

Besides natural colourants, there are a lots of different brands of chemical hair colourants on the market.
and now we're going to reveal how does the chemical hair colourant works.
Let's start with the structure of our hair.
Human hair has a cuticle outer layer of hair shaft.
The hair shaft has to be opened before the hair colourant can be deposited into the hair.
Once the cuticle is open, the colourant reacts with the inner portion of hair, which also known as the cortex. It is to deposit or remove the natural colour of hair.
Most of the colourants use a two-steps process.
The first step is to remove the original colour of the hair, continue with the second step, which is to deposits a new colour into the hair.
Ammonia is the alkaline chemical that opens the cuticle and allows the hair colour to penetrate the cortex of the hair. Furthermore, it also acts as a catalyst when the permanent hair colour comes together with the peroxide.
Peroxide is used as the developer/oxidizing agent.
The developer removes the original colour existed in the hair, then peroxide breaks the chemical bonds in hair, releasing sulphur to accounts the characteristic odor of haircolour.
Lastly, Melanin decolourized the original colour in hair, bonded a new colour into the hair cotex.

And there you're ready to go, with the hair colour you ever wanted. :)

However, there are still failed hair colouring cases like this,
Consult to doctor right away if you experience itchiness, redness, swelling or any other symptoms.
And always do a allergy sensitive test before hair colouring.


References:
About.com, 2010, Hair Color Chemistry-How Haircoloring works, [online] Available from: , [Accessed date: 20th July 2010]
HealthHype.com, no date, Hair Dye Allergies, [online] Available from: , [Accessed date: 20th July 2010]