While many transistor advocates say their amps are neutral, I've yet to hear one that does not impart a coloration- that of brightness and hardness.
Ralph, I have owned three, the Class A Clayton M300 and M200 monoblocks and the Acoustic Imagery Atsah Ncore NC1200 monos. Maybe in comparison to certain tubed amplifiers there is a quality that some may call hardness but, in comparison to other SS amplifiers I have owned and heard, those amps mentioned would not be considered hard-sounding. IMO, none of the three would be considered "bright" sounding.
Unfortunately, I have yet to hear a perfect amplifier since all I have heard have sonic and operational trade-offs. I have owned some quite good SS Class AB amplifiers that have a hint of the brightness/hardness traits you mentioned but that were otherwise excellent. Since I notice this more after my last three amplifiers being Class A designs, and one Class D, I have wondered if maybe I am now more sensitive to crossover effects in class AB designs. In other words, could the "brightness/hardness" effect you point out be a byproduct of the Class AB design that some of the better designers are able to greatly reduce or even eliminate?