Why do chameleons change colour?

The chameleon - nature’s example of Joseph and his Technicolour Dream Coat!

There is this myth that chameleons change colour to blend in with their surroundings, but this is actually not true.

Most of the reason chameleons change colour is as a signal, a visual signal of mood and aggression, territory and mating behaviour.

The way that chameleons actually do this is really molecular – they're molecular masterminds, really. 

If you look at the skin of a chameleon, you find that they have several layers of specialised cells (called chromatophores), and these are the cells that can change the chameleons colour.

Now, how does the chameleon change colour? Well those chromatophores are wired up to the nervous system. They are also sensitive to chemicals that are washing around in the blood stream of the chameleon.

What happens is that the colours are locked away in tiny vesicles, (little sacks inside the cells) that keep them in one place, so the cells don't look coloured. But when a signal comes in from the nervous system or from the blood stream, the granules or vesicles can discharge, allowing the colour to spread out across the cell, and this alters the colour of the cell.

It’s rather like giving the cell a coat of paint!

By varying the relative amount of activity of the different chromatophores in different layers of the skin, it’s like mixing different paints together.

So, for example, if you mix red and yellow, you get orange, and this is how chameleons do this - they mix different contributions of these chromatophores.

It’s a bit like on your television screen. When you mix different colours together on the screen to get the colour that the eye ultimately perceives and so, that’s how the chameleon changes colour, and usually does so to convey its current mood.

So, a calm chameleon is a pale greeny colour. When it gets angry, it might go bright yellow, and when it wants to mate, it basically turns on every possible colour it can, which shows that it’s in the mood!