“Visualize a red star, do you see the color?” feels a little waffly. I’d think you’re likely to get yes, as people imagine they “see” the way others “see” and respond similarly.
By contrast, as seen in an article mentioned here on HN previously (5 years back?), and trialed any number of times since, you can ask them to “picture” or “visualize” something then surprise ask a different attribute that would have to exist if pictured literally.
If someone isn’t expecting this, asking most people “picture a red triangle” … “ok?” … “which way is it pointing?” will elicit an immediate direction (up, down, left right).
In a small subset of people, when not expecting it, the second question gets a long pause, a “What?”, or some other manifestation of not having a literal triangle envisioned with a preexisting direction.
Those metaphorically “picturing” the concept of a red triangle seem to be taking time to decide and layer into their model what concept of direction it should have, while those with aphantasia seem to come back with “what, literally?” or similar indications that “picture” is a figure of speech.
For myself, that HN discussion is the first time I gathered that for other folks “counting sheep” when they were kids wasn’t a metaphor.