It is not. I recently was talking to an artist who told me that if he's drawing a car for example, he can envision everything in front of his minds eye, from any angle he wants. I am completely unable to envision anything at daytime when fully awake.

Yes, if someone imagines red, we can't be sure it's the same, but this is about how some people can do something, and some people can't.

I participated in a study about aphantasia a while ago, and it's pretty clear that I'm pretty much at the end of a spectrum there. There are indeed people who can imagine extremely vivid imagery. I happen to be able to perfectly imagine sounds and music, as well as compose music in my head, which I assume might be something not everyone else can do. With images, it's the complete opposite for me.