I've always taken it to be that the color is unique to the situation/viewer -- a sort of pearlescent void-color that can't be described in any known language, but which just Is. More a physical phenomenon than an actual color, but distinctly hued somehow.
In my headcanon octarine is a colour between orange and deep purple. Sometimes it has a hazy blackish halo.
I think it's described as a "greenish purple" in some of the books.
I've always taken it to be that the color is unique to the situation/viewer -- a sort of pearlescent void-color that can't be described in any known language, but which just Is. More a physical phenomenon than an actual color, but distinctly hued somehow.
I always thought it was something like https://www.moodlight.org/ (set to 60 colors/second) or https://flashing-colors.com/ (set to 100 colors/second).
Note that those are possibly photosensitive epilepsy risks if you turn them up to 60/100.
+1 for the Sir Terry reference.
I suspect many animals experience color quite differently, including seeing infrared/ultraviolet, etc.
No suspicion needed, that's a very well studied fact.
I thought of "The Colour Out of Space".
My thoughts as soon as I saw the title :)