Mics are used for their sound, which is definitely not a sign that they're transparent. It's more a sign that they lend a quality to the sound of the instrument that most others don't. Vocal mics don't necessarily work on strings, percussion or a grand piano but mics used for some instruments don't work well for vocals, either. The way a mic "hears" is different from how we "hear" the sound from an instrument and it's through these differences that we come to consider a recording to sound one way or another. Also, mic placement techniques can be as personal to the person recording the instruments as anything. Listen to an ECM recording of piano (Keith Jarret, Lyle Mays, etc) and then listen to the same performer when someone else records them. Big difference.
Speakers are the interface between the rest of the system and the acoustic space, which means that they can be used to cause the reproduced sound to either work well, or not. An extremely bright speaker may sound great in an acoustically dead room but not in a room without any absorptive materials. What about a listener who has higher/lower acuity at certain frequencies- should they be forced to use "transparent" sounding speakers? I don't think so- I think they should pick a speaker that sounds good to them, regardless of what someone else thinks (unless they're Blose).
Just my opinion.