Tone controls! Curtains, rugs, curtains on the ceiling. Art panels from GIK acoustics. Headphones. Small speakers you can keep far from the walls and into the room.
Bright: B&W, Golden Ear, Focal, Triangle, Thiel, NHT.
Neutralish: Monitor Audio is quite neutral, great if you can use them.
Darker sounding: AR, Boston Acoustics, Bose (no flames). Rega, Monarchy are some of the brands in the past that sounded more mellow. I have various amounts of listening time, and some a lot older than others, so YMWV.
This is all from poor memory and no scientific rigor whatsoever. The flame wars may start, but I mean little harm in my thoughts.
Best,
Erik