Seeing colour is often taken for granted and scientists believe that humans are merely sampling the possible ways of sensing the spectrum of light. Most of us see more colours than dogs but miss millions of colours that make up the world for birds, reptiles, and insects.
Why do we see the colours we do?
As humans evolved, it is believed we inherited colour-absorbing pigments from bacteria more than a billion years ago. The specific colours we see are, in part, an artifact of bacterial needs.
These ancient colour-sensing pigments are tuned to two wavelengths – or cones as we now call them. Shorter ones that correspond to blue and longer ones that go with yellows or reds. All other colour vision we have today is an outgrowth of that system.
In humans, mutations on the X chromosome can interfere with this human evolution. Most people who are considered colour-blind (colour blindness — or more specifically have a colour vision deficiency (CVD)) have the same colour capacity as dogs and cats and can’t distinguish red and green. The term red-green colour blindness is often used but is not quite correct. Every type of colour vision deficiency affects the whole colour spectrum and, therefore cannot be reduced to certain colours. Of course, for the most often encountered types:
Protanomly (the milder form or red weakness) or Protanopia (missing red cones, red blindness)
Deuteranomaly (green weakness)
Deuteranopia (green blindness) the colours red and green are the most problematic and misinterpreted or indistinguishable ones.
But people suffering from any of those forms have issues with the red or green part in every colour, so the whole colour is affected.
Men are much more likely to inherit this type of colour because they only have one copy of the X chromosome, while women have a second X as a backup. 
Besides red-green colour blindness, which is encoded on the x-chromosome (sex-linked) and therefore much more common for men, there are also forms of colour vision deficiency that are evenly distributed between males and females like Tritanomaly (blue-weakness) or Tritanopia (blue-blindness) and the real colour blindness Achromatopsia (monochromacy) or the so-called blue-cone monochromacy (only blue cones).
We are lucky to live in this day and age where people accept people’s differences. Though people with colour vision deficits experience difficulties in daily life, early learning and development, education, choice of careers, and work performance. Current technology like our iRo Lenses along with optical devices, visual aids, and technology apps can allow them to live better and adapt with their colour deficiency.
