The iris, which makes up the colour of our eyes, has deposits of melanin. Melanin is a colour pigment that is not only responsible for the colour of our eyes, but also for our hair and skin colour. Depending on how much melanin is stored in the iris, a different eye colour develops.
Melanin can reflect or absorb certain wavelengths of light, depending on the degree to which it does so, the three classic eye colours blue, brown and green are created. The melanin in our eyes serves as protection against sunlight. Accordingly, one stimulus for melanin production is the contact of the eyes with sun rays, so that melanin production is only really stimulated during the first years of life and consequently the eye colour can still change.
Causes for a lighter eye colour
For a light eye colour like blue, you need relatively little pigment. The less melanin is stored in the eyes, the lighter the eyes appear. People with light eye colours inherit genes that have little or no ability to produce melanin. Since melanin is a protective factor against sunlight, people with blue or light eyes are more sensitive to light. If a little more pigment is stored than in blue eyes, green eyes develop.
When is the final eye colour created?
Newborn babies usually have blue eyes in the beginning, or rather eyes that look blue. This is because babies’ eyes are not really blue. This is due to the fact that the iris of the eye, which is responsible for the colour of the eyes, only absorbs a few rays of light in babies, because until now only a few pigments/less melanin have been stored.
The consequence is that many light rays are thrown back again because absorption cannot yet take place. The iris therefore appears blue. The final eye colour develops with half a year to one year, at the latest with one and a half years the final eye colour should be developed. If babies with blue eyes still have small dark or brown spots, this indicates that the eye colour is still changing. Even if the basic eye colour has already been defined after about one year, different shades and gradations of the basic colour blue, grey, brown or green can still occur with increasing age, so that individual eye colours emerge.
Can you influence the eye colour of the baby?
You cannot influence the eye colour of the baby, as it is genetically determined. The genetic make-up determines how much dye melanin is produced. This is ultimately responsible for the pigmentation of the iris in the eye and thus for the eye colour of the baby.
It is also assumed that there is an evolutionary-biological connection with eye colour. In areas with a lot of sunlight (e.g. Africa, Southern Europe) the population has dark eyes on average, in colder areas (e.g. Scandinavia) blue eyes are more common. Dark eyes are a protection against the sun and have thus probably become established in Africa, among other places.