I'd seen a little about this previously, but this is a really good story on color perception and the scientific tricks used to let a very small number of people see a new color that doesn't exist in nature.
What Would It Mean to See a New Color?
A new color called olo can be described as the “greenest green.” It can never be captured by a camera, but its development tells us a lot about how vision works.
newyorker.com