The world of ISAT is fully monochrome. As in, in-universe. You can find multiple mentions that there used to be colors in this world, but they all vanished for some reason and now everything is in grayscale.

I often see people wondering why colors vanished. Personally, I don't really care. I'm fine with wacky worldbuildings being like "oh yeah btw this thing happened and we're never gonna elaborate on that." The bit that interests me, however, is how did they discover colors again? Did they find fossilized colors under a rock dinosaur-style?

Bonnie knew the names of some colors ("bloo" and "grin") as well as what they represented, so my theory is that the color discovery was at least partially based on studying ancient stories. I mean, if 20 different civilisations all have ancient texts that describe the sky with a recurring adjective, you'd be looking into it too, right?