Egg colour- white, brown, speckled, blue - what makes the difference?

Chickens eggs come in all kinds of colours – brown, white, pale creamy colour. Some with spots or speckles. Even blue eggs! So what makes the colour? And do we get brown eggs from brown chooks, and white eggs from white chooks? No, not really. But you can get an idea of what colour eggs a hen might lay by looking at her earlobes! The association between the colour of the earlobes and the colour of the eggs doesn’t always work, because there is actually no genetic link between the genes for earlobe colour and the genes for egg shell colour. However, it’s a pretty good rule of thumb for the purebred heritage breeds that we have in New Zealand.
If you look inside the eggshell you can see that the brown colour is just on the outside, the inside of a brown eggshell is white. The brown colour comes from a coating that the hen puts on the outside of the shell while it is in the oviduct. It takes about 26 hours for a hen to make an egg and most of that time is actually spent making the shell. Right at the end, during the last few hours, the colour is put on – it comes from a substance called protoporphyrin, which is related to the heme in haemoglobin – the stuff that makes our blood cells red. If the coating goes on unevenly, we get an egg that has spots or speckles.
Whatever colour eggs a hen lays, she pretty much lays the same colour all the time. There is a tendency for her eggs to get paler throughout the laying season, and then start off darker again after her break from laying eggs during the moult.
The blue colour of blue eggs comes a from a pigment called oocyanin. The hen adds oocynanin all the way throughout the twenty hours or so of making the egg shell, so the egg shell is blue all the way through.
If a hen that makes a blue egg then applies a brown coating the outside of the shell, the brown on top of the blue makes the egg look green.
If you want a colourful nest box, just choose a mixture of hens that lay different coloured eggs.

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