Not what I said though. The amateur witness is not likely to think about what colour the other side is, and not likely to accurately report what they saw. It's not about them saying what the colour of the rest of the car is, especially as that's a trivial example. It's about accurately identifying what you really saw, and distinguishing it from how the brain interpreted, or remembers, what you saw.
It is sometimes, perhaps often, both useful and desirable to have "pedantic" witnesses that accurately report what they really do see, and get it right, without reporting what they thought they saw, but didn't. For instance, if reporting a crime to the police, just as accurate evidence is useful, inaccurate accounts, however well-intentioned, can be harmful and end up wasting police time, or even helping to convict the wrong person.