Say you have a sixteen-year-old human boy who is born with infrared vision. Allowing for severe mutation or Brilliant Mad Scientist of Doom (plus maybe a little fudging), is this even possible? How exactly would this work with his normal, human physiology? What would he look like?
Assuming the boy can only see in infrared, I'm having trouble figuring out what certain things would look like to him. Would visible light vision have crossed over with infrared if he hadn't lost it? Could he read a book? Read at all? Admire a painting? What would a blistering hot day be to him? What would a frosty one? What would a view out of the window look like if the glass is warm or cold? What will people think of a boy who can't 'see' colors or letters, but can see people and objects? Could I get away with a kid who can't see visible light and not have any of his parents or teachers know exactly what's wrong with him? His family's pretty much broke, and they live in a very poor, rural area.
Now, on to what I do know, just in case any of it is wrong and I need correcting. Snakes and lizards see with little pits in their heads. Electronics screens will be warm squares of nothing. A chalkboard or whiteboard will be a similar mystery. If someone is running a fever, he'll be able to tell, and he can see if an injury is infected because it's a bit hotter than usual. Facial features will be distinct enough in his vision to tell them apart. (I'm really iffy on that one.) If he's looking at a white sign with large black letters on it that have been in the sun a while, he can see the letters. Correct my inaccuracies where you find them; I love being wrong.
I am so ignorant, and you are all so smart and helpful. Thank you so much for your assistance!