“Neutral” is up there with “accurate” as the most misused terms in audio. Les McCaan, indeed; compared to what?
Some misuse the two terms to describe a sound that, to me, is lean, too bright and often bleached out. The.terms should be used to describe a component that neither adds nor subtracts anything from the signal as it passes through it on the way to the next component in the system, or, in the case of speakers, to the listener’s ears. As has been pointed out, true neutrality, or accuracy, are very lofty goals and ultimately unattainable since every component alters the signal to some degree. However, some components do an infinitely better job than others of preserving signal integrity.
The sound of live acoustic (not amplified) instruments and voice have a lot of natural color and warmth. Their sound is not colorless (bleached) which is what many think a “neutral” sound is. It is not true that the sound of live acoustic music cannot be used as a reference for judging the sound of a component. The key is to think in terms of degree of electronic signature that the component adds. The sound of live acoustic music has zero electronic signature, The component that adds less electronic signature to the sound can be said be closer to neutral than the component that adds more electronic signature. With recordings of electronic (amplified) instruments all bets are off.