Piano and Trumpet can sound bright

It must be said that both of those instruments are quite bright naturally, especially the trumpet. But many pianos are too, especially the Yamahas that are in wide use today.

In the vast majority of jazz clubs, the performers are miked. This is actually what creates most of the brightness, the sound systems are just too damn loud. There may be some clubs in NYC still that don't mike, but there sure aren't many anywhere else. That said, even with a performer that strives for a dark trumpet sound, which for instance most orchestral players do, it is still a bright instrument compared to most others. And most jazz trumpet players are not necessarily striving for a dark sound - a lead player in a dance band quite the opposite, for instance.