The colour of an object we see is based upon light refracted back. So if an object is black it is absorbing most of the light, and the classic grass - which appears green is actually absorbing the red and blue spectrum and reflecting back the green light - appearing green.
"Are dark objects dark just because the light they emit are in an invisible frequency range?" the light they reflect back may well encompass the non visible spectrum, after all that's how radar works and the drive for radar absorbing materials by the military. So not all objects that for us in out limited light spectrum visual senses are equal, even if they look the same - black. May be one reflects back UV, one may absorb it. So for a true picture you would need to see an absorption graph of the full spectrum (visible and non visible).
Crux is - objects we see via refracted light - we are seeing in negative. So whilst we see green grass, it's true colour is everything but green.
>So whilst we see green grass, it's true colour is everything but green.
I've never liked this phrasing. In what sense is the "true" color not green if we perceive green? It is the color it reflects, it's just a little counter-intuitive when you first learn of the physics behind it.
Yes I will conceed it is far from an ideal way of describing how things are and with that, somewhat subjective in perception.
For me, it gets down to physics and how we perceive things. From a human perception aspect - the true colour of grass is green. But when you add the science aspect, it is not that clear cut. Somewhat gets down to context.
For me - if an object emits light - that's it's true colour. Equally how it refracts light is the perceived colour. Objects that emit light have a true and perceived colour the same. Though there is always other factors like whats in between the object and the light (be that refracted or emitted). The sun and sky being good example of that at play. But equally even at a small scale, the air will have an impact, even if we can not perceive it.
But yes, we're all human and with that, you are right in that the true colour from our perception shows grass is green. So I'll try and refer to grass as its true colour of green and it's physics colour as red/blue.
Which feels perhaps a better way of phrasing and one I'll try and run with until something better comes along.
