On the subject of blindness: What we are able to experience is limited by our biology. This differs from the view that our eyes, ears, and fingers receive an objective physical world outside of ourselves. Our brains sample a small bit of the surrounding physical world.
At the beginning of the last century biologists noticed that different animals in the same ecosystem picked up different signals from their environment. In the blind and deaf world of the tick the important signals are temperature and the odor of butyric acid. For the black ghost knifefish, it is electrical signals. For the bat it is air-compression. Biologists introduced a new concept: the part that you are able to see, the environment or surrounding world, they call the umwelt and the bigger reality, if there is such a thing, they called the umgebung.
Each organism has its own umwelt, which it assumes to be the entire objective reality out there.
Ask yourself what would it be like to have been blind from birth. If your guess is "it would be something like blackness" or "something like a dark hole where vision should be," you would be wrong. Imagine you are a scent dog such as a bloodhound. Your long nose would contain two hundred million receptors. On the outside, your wet nostrils attract and trap scent molecules. The slits at the corners or each nostril flare out to allow more air flow as you sniff. Your floppy ears drag along the ground and kick up scent molecules. Your world is smelling. You wonder what it must be like to have the pitiful, impoverished nose of a human being. What could humans possibly detect when they take in a feeble little nose of air? Do they suffer a blackness? A hole of smell where smell is supposed to be?
Because you are human you know the answer is no. There is no hole or blackness or a missing feeling where the scent is absent. You accept your reality as it is presented to you. Because you do not have the smelling capabilities of a bloodhound, it doesn't occur to you that things could be different. The same goes of people with color blindness: until they learn that others can see hues they cannot, the thought does not appear on their radar.
A fraction of women have not just three but four photoreceptors---and as a result they can distinguish colors that the majority of men and women will never differentiate. If you are not a member of that small female population, then you have just discovered something about your own impoverishments that you were unaware of. You may not have thought yourself to be color-blind, but to those ladies supersensitive to hues, you are. In the end, it does not ruin your day; instead, it only makes you wonder how someone else can see the world so strangely. One can only imagine the number of divorces that fourth photo-receptor has caused.
And so it goes for the congenitally blind. They are not missing anything; they do not see blackness where vision is missing. Vision was never part of their reality in the first place, and they miss it only as much as you miss the extra scents of the bloodhound dog or the extra colors of the tetrachromatic women.
