In our world people and animals, all perceive colour differently. When people hear that someone is colour blind, they often think it means they see only in black and white. In truth, they face colour vision problems. And experience a colour deficiency or confusion between colours.
Though most colour blind people can distinguish some colours, it is just that some are more difficult to differentiate than others. That is why we prefer to use the term colour deficient rather than colour blind.
Human eyes contain three types of colour detecting cells: red-detecting cones, green-detecting cones, and blue-detecting cones. Each cone cell can detect many colours in addition to its main colour. For instance, the cone cells in the eye that can see red light can also see orange and yellow. The red cone cells just see red the best, and that is why they are called the red cones.
Similarly, the green cones can also see orange, yellow and blue. This overlap is what allows us to see so many different colours. We can see the colour yellow, for instance, even though there are no yellow receptors, because of this overlap. When you look at a yellow flower, the yellow light stimulates the red and green cells in your eyes, and your brain interprets a little bit of red plus a little bit of green as yellow.
When a person with full vision looks at the blue sky, it is not just the blue cone cells that are stimulated. It is like a colour palette where the blue cone cells are stimulated and so are green cone cells, but at different quantities ie 75% and 25%. Our brains experience pure blue as a large blue cell signal plus a small green cell signal due to responses overlapping.
With a blue colour vision deficit person, they have tritanopia which means they are missing the blue-detecting cells in their eyes. So when they look at the blue sky, the blue cells don’t see anything because they are missing. Imagine trying to mix paint to paint something blue and you don’t have any blue colour to do it. A person with full vision sees the colours green, blue, and violet, a person with blue colour blindness sees these colours as green, dark green, and darker green. They see colour, but just see the colours slightly wrong and has a harder time telling certain colours apart
The green-detecting cells are still there, and they see blue a little bit. That is why a typical colour vision deficit person blind person is not really completely blind to any colour. A person with blue colour blindness experiences pure blue as dark green. The colour perception is not complete and not quite right, but they do experience colour, even in the colour range where they have the greatest difficulty.
Another example is when a person with blue colour blindness looks at pink, only the blue part of the colour mixture is faulty, which is a small part of the colour pink. As a result, pink looks nearly normal to a person with blue colour blindness. The same goes for other colours that are a mixture of fundamental colours.