Noumenon and phenomenon

From Is Anything Certain in Science? by Alex B. Berezow.

Philosopher Immanuel Kant wrote of the noumenon (actual reality) and the phenomenon (our experience of reality). Because we experience reality through our imperfect senses, we do not have direct access to it. For instance, we perceive plants as green, but that is simply the result of our eyes and brains processing photons and interpreting them as the color green. How do we know that perception is reliable? Isn't it possible that plants are actually some other color? Given that we are limited by our sensory capabilities, we can never know the answer to that question. Our experience of the greenness of a plant (phenomenon) is separate from the underlying reality of a plant's color (noumenon).