I traded in a Yamaha C7 for a Bosendorfer 225 because the C7 was too "bright" for the small space. The sound just started to annoy me. The Bosendorfer, with its spruce rim, is probably among the most mellow pianos you can get. Other ones to consider are the Yamaha S6 (or S4), or the Grotrian 225. It's hard to say if what's "dark" to me is dark to you, but all of these have notes that hang around for a while, and more of the fundamental tone sustaining over time.

I am surprised Mason & Hamlin has not come up in this thread. Their new instruments may be somewhat brighter than their golden age ones perhaps, but there's a depth and richness in the M&H tonal ideal that some might call dark or mellow.

Grotrian is the only piano that Larry Fine qualifies "dark" in his book The Piano Book that you can find online

Hello
I would describe the sound of my Grotrian 225 as warm and dark especially in the mid range. May be comparable to the sound of a Boesendorfer of similar size in which the Boesendorfer seems to be a little bit more "refined". On the other side of the spectrum I see the new C.Bechsteins:
very clear and "transparent" but not at all "cold". But: I'm not an expert and this is my very subjective feeling.

Based on my experience playing Blüthner, Bösendorfer, C. Bechstein, Grotrian-Steinweg, Kawai, Yamaha and Steinway grands, Blüthner is easily the most mellow and dark in tone. It's also apparent on CD recordings (Mikhail Pletnev and Artur Pizarro are Blüthner pianists).

I once played an old Feurich grand, and I fell in love with it's dark, vocal, mellow. It wasn't particularly powerful, but it was nice. It was unrestored, and being 97 years old at the time, it was actually in pretty good shape. Just mentioning it, as it seemed to fit the description of "dark and mellow".

But they are nowhere near as bright as they were, maybe 10-15 years ago. These were the first Masons I ever played, and it wasn't a good impression. Of course, the pianos have changed a lot since then, and now I'm a big fan.

If you have room for a 7ft 2in, here's a snippet of my "home recording" of it.... might give you some idea of the sound:

http://www.box.com/s/28llz3nl7f757z0tlr2n

Here's a processed version of the same file: http://www.box.com/s/pcgjnn7zba2vimx4ma2o

Room humidity constant at 42; no tuning stability issues so far (6 months); touch permits very soft playing, absent using soft pedal. Overtones complex.

I like it. Oh... forgot....it's a Hailun 218 squeezed into 14x11ish space with large french doors to open up more when the family is out!

JG