The second way would be to abstractly build a car in my mind. Start with four tires, put a rough shape of a frame on it — lets make it a sedan. If I proceed this way, I probably would not choose a color, at least not early on. Like many in this thread, this is how I usually imagine things, as "wireframes". The color/texture is not there because I have not assigned it. I can't vividly see the things I imagine, but they can still have color just like they can have shape.
If I imagine a car, I can imagine its features, and of course color being a quite salient feature I would probably assign it a color (e.g. I could imagine a red Ferrari, or a black limo). It's just that I wouldn't see it, there wouldn't be anything in my mind similar to the actual experience of seeing a red object, I would just think about the "concept" of the car being red (hard to explain).
So far I've never found a way in which aphantasia really manifests externally or can be measured externally in a more or less reliable way. Which is why I'm still not 100% sure that people who claim not to be aphantasiacs aren't just exaggerating or taking metaphors too literally...
I can't recall anything I didn't actively notice while looking. If you stop me when I'm leaving a grocery store and ask me questions about the cashier, I won't be able to tell you their hair color or what kind of clothes they were wearing. Sometimes I won't even be able to tell you if they were tall or fat or any other physical adjectives.
For example, you can ask "most people" to imagine a car, and then follow up by asking "what color did you imagine it?". For me and you this question would not make any sense, but you'll find out that "most people" find it completely normal and answer it without questioning you.