A neutral transparent speaker can sound plain. It often would be easy to just walk on by such a speaker. Notice how they often close mike musical instruments and singers to capture more richness. I had some speakers with a TPX plastic cone. They gave a very pleasant richness and tone to stringed instruments. I went to my classical guitar and couldnt duplicate that richness. My guitar sounded plain in comparison. I would call that warmth. My speakers are transparent so I usualy like a tubed preamp and vinyl to add warmth.
Bob
Bob